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 $59.91   13.258%   $67.8529   $67.85   $67.85   $67.90  
  Purchase #2 $161.28   12.871%   $182.0383   $182.04   $182.05   $182.00  
  Purchase #3 $182.74   7.719%   $196.8457   $196.85   $196.85   $196.80  
  Purchase #4 $23.98   9.187%   $26.183   $26.18   $26.20   $26.20  
  Purchase #5 $211.72   11.196%   $235.4242   $235.42   $235.40   $235.40  
  Purchase #6 $219.93   9.132%   $240.014   $240.01   $240.00   $240.00  
  Purchase #7 $250.58   3.306%   $258.8642   $258.86   $258.85   $258.90  
  7 purchase totals = $1,110.14       $1,207.2223   $1,207.21   $1,207.20   $1,207.20