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 $62.48   11.576%   $69.7127   $69.71   $69.70   $69.70  
  Purchase #2 $112.48   8.436%   $121.9688   $121.97   $121.95   $122.00  
  Purchase #3 $160.76   8.567%   $174.5323   $174.53   $174.55   $174.50  
  Purchase #4 $146.82   7.115%   $157.2662   $157.27   $157.25   $157.30  
  Purchase #5 $164.33   11.737%   $183.6174   $183.62   $183.60   $183.60  
  Purchase #6 $164.71   5.439%   $173.6686   $173.67   $173.65   $173.70  
  Purchase #7 $45.53   5.797%   $48.1694   $48.17   $48.15   $48.20  
  7 purchase totals = $857.11       $928.9354   $928.94   $928.85   $929.00