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 $103.69   10.730%   $114.8159   $114.82   $114.80   $114.80  
  Purchase #2 $159.28   7.319%   $170.9377   $170.94   $170.95   $170.90  
  Purchase #3 $83.94   12.794%   $94.6793   $94.68   $94.70   $94.70  
  Purchase #4 $97.49   6.163%   $103.4983   $103.50   $103.50   $103.50  
  Purchase #5 $116.56   6.391%   $124.0093   $124.01   $124.00   $124.00  
  Purchase #6 $35.29   7.729%   $38.0176   $38.02   $38.00   $38.00  
  Purchase #7 $127.33   5.854%   $134.7839   $134.78   $134.80   $134.80  
  7 purchase totals = $723.58       $780.7420   $780.75   $780.75   $780.70