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 $30.65   7.524%   $32.9561   $32.96   $32.95   $33.00  
  Purchase #2 $195.33   7.334%   $209.6555   $209.66   $209.65   $209.70  
  Purchase #3 $140.78   12.775%   $158.7646   $158.76   $158.75   $158.80  
  Purchase #4 $108.45   12.685%   $122.2069   $122.21   $122.20   $122.20  
  Purchase #5 $204.36   3.159%   $210.8157   $210.82   $210.80   $210.80  
  Purchase #6 $116.42   9.841%   $127.8769   $127.88   $127.90   $127.90  
  Purchase #7 $153.62   5.213%   $161.6282   $161.63   $161.65   $161.60  
  7 purchase totals = $949.61       $1,023.9039   $1,023.92   $1,023.90   $1,024.00