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 $192.94   4.396%   $201.4216   $201.42   $201.40   $201.40  
  Purchase #2 $239.99   9.863%   $263.6602   $263.66   $263.65   $263.70  
  Purchase #3 $243.67   13.434%   $276.4046   $276.40   $276.40   $276.40  
  Purchase #4 $125.62   11.840%   $140.4934   $140.49   $140.50   $140.50  
  Purchase #5 $105.64   13.352%   $119.7451   $119.75   $119.75   $119.70  
  Purchase #6 $151.98   9.779%   $166.8421   $166.84   $166.85   $166.80  
  Purchase #7 $157.44   4.689%   $164.8224   $164.82   $164.80   $164.80  
  7 purchase totals = $1,217.28       $1,333.3894   $1,333.38   $1,333.35   $1,333.30