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 $235.97   4.790%   $247.273   $247.27   $247.25   $247.30  
  Purchase #2 $110.38   5.574%   $116.5326   $116.53   $116.55   $116.50  
  Purchase #3 $35.36   12.409%   $39.7478   $39.75   $39.75   $39.70  
  Purchase #4 $192.53   10.283%   $212.3279   $212.33   $212.35   $212.30  
  Purchase #5 $14.35   7.380%   $15.409   $15.41   $15.40   $15.40  
  Purchase #6 $173.76   3.132%   $179.2022   $179.20   $179.20   $179.20  
  Purchase #7 $123.28   6.475%   $131.2624   $131.26   $131.25   $131.30  
  7 purchase totals = $885.63       $941.7549   $941.75   $941.75   $941.70