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 $85.48   11.376%   $95.2042   $95.20   $95.20   $95.20  
  Purchase #2 $70.73   3.833%   $73.4411   $73.44   $73.45   $73.40  
  Purchase #3 $90.96   10.809%   $100.7919   $100.79   $100.80   $100.80  
  Purchase #4 $138.47   8.749%   $150.5847   $150.58   $150.60   $150.60  
  Purchase #5 $110.32   13.771%   $125.5122   $125.51   $125.50   $125.50  
  Purchase #6 $200.41   4.787%   $210.0036   $210.00   $210.00   $210.00  
  Purchase #7 $112.87   11.496%   $125.8455   $125.85   $125.85   $125.80  
  7 purchase totals = $809.24       $881.3832   $881.37   $881.40   $881.30