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 $182.43   7.822%   $196.6997   $196.70   $196.70   $196.70  
  Purchase #2 $121.74   10.352%   $134.3425   $134.34   $134.35   $134.30  
  Purchase #3 $35.38   13.437%   $40.134   $40.13   $40.15   $40.10  
  Purchase #4 $207.79   8.351%   $225.1425   $225.14   $225.15   $225.10  
  Purchase #5 $202.39   5.472%   $213.4648   $213.46   $213.45   $213.50  
  Purchase #6 $51.73   3.210%   $53.3905   $53.39   $53.40   $53.40  
  Purchase #7 $178.66   12.787%   $201.5053   $201.51   $201.50   $201.50  
  7 purchase totals = $980.12       $1,064.6793   $1,064.67   $1,064.70   $1,064.60