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 $249.96   10.485%   $276.1683   $276.17   $276.15   $276.20  
  Purchase #2 $241.42   12.339%   $271.2088   $271.21   $271.20   $271.20  
  Purchase #3 $73.45   3.412%   $75.9561   $75.96   $75.95   $76.00  
  Purchase #4 $179.73   6.791%   $191.9355   $191.94   $191.95   $191.90  
  Purchase #5 $141.95   9.845%   $155.925   $155.93   $155.95   $155.90  
  Purchase #6 $133.43   10.179%   $147.0118   $147.01   $147.00   $147.00  
  Purchase #7 $61.43   6.427%   $65.3781   $65.38   $65.40   $65.40  
  7 purchase totals = $1,081.37       $1,183.5836   $1,183.60   $1,183.60   $1,183.60