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 $165.81   6.362%   $176.3588   $176.36   $176.35   $176.40  
  Purchase #2 $138.52   12.103%   $155.2851   $155.29   $155.30   $155.30  
  Purchase #3 $219.82   3.499%   $227.5115   $227.51   $227.50   $227.50  
  Purchase #4 $42.76   6.282%   $45.4462   $45.45   $45.45   $45.40  
  Purchase #5 $228.57   6.203%   $242.7482   $242.75   $242.75   $242.70  
  Purchase #6 $34.73   12.823%   $39.1834   $39.18   $39.20   $39.20  
  Purchase #7 $129.33   6.770%   $138.0856   $138.09   $138.10   $138.10  
  7 purchase totals = $959.54       $1,024.6188   $1,024.63   $1,024.65   $1,024.60