Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $98.32   12.110%   $110.2266   $110.23   $110.25   $110.20  
  Purchase #2 $111.91   11.567%   $124.8546   $124.85   $124.85   $124.90  
  Purchase #3 $237.46   11.330%   $264.3642   $264.36   $264.35   $264.40  
  Purchase #4 $178.84   13.653%   $203.257   $203.26   $203.25   $203.30  
  Purchase #5 $210.87   11.613%   $235.3583   $235.36   $235.35   $235.40  
  Purchase #6 $224.41   5.321%   $236.3509   $236.35   $236.35   $236.40  
  Purchase #7 $170.30   5.622%   $179.8743   $179.87   $179.85   $179.90  
  7 purchase totals = $1,232.11       $1,354.2859   $1,354.28   $1,354.25   $1,354.50