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 $81.54   8.142%   $88.179   $88.18   $88.20   $88.20  
  Purchase #2 $66.34   12.457%   $74.604   $74.60   $74.60   $74.60  
  Purchase #3 $124.27   6.514%   $132.3649   $132.36   $132.35   $132.40  
  Purchase #4 $242.95   10.564%   $268.6152   $268.62   $268.60   $268.60  
  Purchase #5 $11.31   5.517%   $11.934   $11.93   $11.95   $11.90  
  Purchase #6 $66.87   10.367%   $73.8024   $73.80   $73.80   $73.80  
  Purchase #7 $20.92   7.718%   $22.5346   $22.53   $22.55   $22.50  
  7 purchase totals = $614.20       $672.0341   $672.02   $672.05   $672.00