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 $212.32   11.140%   $235.9724   $235.97   $235.95   $236.00  
  Purchase #2 $188.35   10.656%   $208.4206   $208.42   $208.40   $208.40  
  Purchase #3 $11.37   11.832%   $12.7153   $12.72   $12.70   $12.70  
  Purchase #4 $141.82   13.456%   $160.9033   $160.90   $160.90   $160.90  
  Purchase #5 $116.85   13.610%   $132.7533   $132.75   $132.75   $132.80  
  Purchase #6 $233.76   5.746%   $247.1918   $247.19   $247.20   $247.20  
  Purchase #7 $41.49   11.224%   $46.1468   $46.15   $46.15   $46.10  
  7 purchase totals = $945.96       $1,044.1035   $1,044.10   $1,044.05   $1,044.10