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 $92.60   6.194%   $98.3356   $98.34   $98.35   $98.30  
  Purchase #2 $66.44   3.190%   $68.5594   $68.56   $68.55   $68.60  
  Purchase #3 $57.36   5.787%   $60.6794   $60.68   $60.70   $60.70  
  Purchase #4 $200.30   5.281%   $210.8778   $210.88   $210.90   $210.90  
  Purchase #5 $56.88   5.262%   $59.873   $59.87   $59.85   $59.90  
  Purchase #6 $104.90   5.140%   $110.2919   $110.29   $110.30   $110.30  
  Purchase #7 $231.49   10.622%   $256.0789   $256.08   $256.10   $256.10  
  7 purchase totals = $809.97       $864.6960   $864.70   $864.75   $864.80