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 $201.61   12.732%   $227.279   $227.28   $227.30   $227.30  
  Purchase #2 $30.90   5.778%   $32.6854   $32.69   $32.70   $32.70  
  Purchase #3 $86.90   6.298%   $92.373   $92.37   $92.35   $92.40  
  Purchase #4 $182.51   9.313%   $199.5072   $199.51   $199.50   $199.50  
  Purchase #5 $70.53   6.253%   $74.9402   $74.94   $74.95   $74.90  
  Purchase #6 $232.34   4.834%   $243.5713   $243.57   $243.55   $243.60  
  Purchase #7 $125.41   4.623%   $131.2077   $131.21   $131.20   $131.20  
  7 purchase totals = $930.20       $1,001.5638   $1,001.57   $1,001.55   $1,001.60