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 $228.99   10.816%   $253.7576   $253.76   $253.75   $253.80  
  Purchase #2 $27.45   6.411%   $29.2098   $29.21   $29.20   $29.20  
  Purchase #3 $64.80   7.845%   $69.8836   $69.88   $69.90   $69.90  
  Purchase #4 $244.56   12.629%   $275.4455   $275.45   $275.45   $275.40  
  Purchase #5 $163.62   6.554%   $174.3437   $174.34   $174.35   $174.30  
  Purchase #6 $121.62   9.710%   $133.4293   $133.43   $133.45   $133.40  
  Purchase #7 $54.72   13.436%   $62.0722   $62.07   $62.05   $62.10  
  7 purchase totals = $905.76       $998.1417   $998.14   $998.15   $998.10