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 $123.73   8.419%   $134.1468   $134.15   $134.15   $134.10  
  Purchase #2 $193.32   5.292%   $203.5505   $203.55   $203.55   $203.60  
  Purchase #3 $215.28   9.622%   $235.9942   $235.99   $236.00   $236.00  
  Purchase #4 $190.63   4.453%   $199.1188   $199.12   $199.10   $199.10  
  Purchase #5 $224.96   13.765%   $255.9257   $255.93   $255.95   $255.90  
  Purchase #6 $151.80   12.873%   $171.3412   $171.34   $171.35   $171.30  
  Purchase #7 $60.51   5.198%   $63.6553   $63.66   $63.65   $63.70  
  7 purchase totals = $1,160.23       $1,263.7325   $1,263.74   $1,263.75   $1,263.70