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 $32.56   8.607%   $35.3624   $35.36   $35.35   $35.40  
  Purchase #2 $214.79   5.783%   $227.2113   $227.21   $227.20   $227.20  
  Purchase #3 $61.63   5.249%   $64.865   $64.87   $64.85   $64.90  
  Purchase #4 $166.71   7.232%   $178.7665   $178.77   $178.75   $178.80  
  Purchase #5 $75.75   3.118%   $78.1119   $78.11   $78.10   $78.10  
  Purchase #6 $165.96   12.322%   $186.4096   $186.41   $186.40   $186.40  
  Purchase #7 $221.51   4.736%   $232.0007   $232.00   $232.00   $232.00  
  7 purchase totals = $938.91       $1,002.7274   $1,002.73   $1,002.65   $1,002.80