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 $30.92   5.731%   $32.692   $32.69   $32.70   $32.70  
  Purchase #2 $225.48   5.182%   $237.1644   $237.16   $237.15   $237.20  
  Purchase #3 $7.90   9.370%   $8.6402   $8.64   $8.65   $8.60  
  Purchase #4 $21.31   12.832%   $24.0445   $24.04   $24.05   $24.00  
  Purchase #5 $104.76   13.585%   $118.9916   $118.99   $119.00   $119.00  
  Purchase #6 $125.46   9.227%   $137.0362   $137.04   $137.05   $137.00  
  Purchase #7 $42.45   8.342%   $45.9912   $45.99   $46.00   $46.00  
  7 purchase totals = $558.28       $604.5601   $604.55   $604.60   $604.50