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 $201.68   8.241%   $218.3004   $218.30   $218.30   $218.30  
  Purchase #2 $230.44   3.681%   $238.9225   $238.92   $238.90   $238.90  
  Purchase #3 $224.82   5.103%   $236.2926   $236.29   $236.30   $236.30  
  Purchase #4 $147.29   6.386%   $156.6959   $156.70   $156.70   $156.70  
  Purchase #5 $234.86   3.642%   $243.4136   $243.41   $243.40   $243.40  
  Purchase #6 $43.71   4.319%   $45.5978   $45.60   $45.60   $45.60  
  Purchase #7 $205.48   5.118%   $215.9965   $216.00   $216.00   $216.00  
  7 purchase totals = $1,288.28       $1,355.2193   $1,355.22   $1,355.20   $1,355.20