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 $183.58   11.342%   $204.4016   $204.40   $204.40   $204.40  
  Purchase #2 $120.67   4.184%   $125.7188   $125.72   $125.70   $125.70  
  Purchase #3 $69.75   9.733%   $76.5388   $76.54   $76.55   $76.50  
  Purchase #4 $188.60   6.764%   $201.3569   $201.36   $201.35   $201.40  
  Purchase #5 $149.65   13.265%   $169.5011   $169.50   $169.50   $169.50  
  Purchase #6 $139.40   9.644%   $152.8437   $152.84   $152.85   $152.80  
  Purchase #7 $55.89   13.241%   $63.2904   $63.29   $63.30   $63.30  
  7 purchase totals = $907.54       $993.6513   $993.65   $993.65   $993.60