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 $85.61   7.709%   $92.2097   $92.21   $92.20   $92.20  
  Purchase #2 $223.98   8.461%   $242.9309   $242.93   $242.95   $242.90  
  Purchase #3 $159.57   5.795%   $168.8171   $168.82   $168.80   $168.80  
  Purchase #4 $22.37   10.598%   $24.7408   $24.74   $24.75   $24.70  
  Purchase #5 $20.99   9.859%   $23.0594   $23.06   $23.05   $23.10  
  Purchase #6 $52.30   9.323%   $57.1759   $57.18   $57.20   $57.20  
  Purchase #7 $141.52   7.105%   $151.575   $151.58   $151.60   $151.60  
  7 purchase totals = $706.34       $760.5088   $760.52   $760.55   $760.50