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 $17.32   10.764%   $19.1843   $19.18   $19.20   $19.20  
  Purchase #2 $135.67   12.492%   $152.6179   $152.62   $152.60   $152.60  
  Purchase #3 $226.62   12.562%   $255.088   $255.09   $255.10   $255.10  
  Purchase #4 $179.50   3.282%   $185.3912   $185.39   $185.40   $185.40  
  Purchase #5 $190.82   3.299%   $197.1152   $197.12   $197.10   $197.10  
  Purchase #6 $86.49   7.657%   $93.1125   $93.11   $93.10   $93.10  
  Purchase #7 $109.71   10.658%   $121.4029   $121.40   $121.40   $121.40  
  7 purchase totals = $946.13       $1,023.9120   $1,023.91   $1,023.90   $1,023.90