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 $76.86   8.480%   $83.3777   $83.38   $83.40   $83.40  
  Purchase #2 $215.63   13.543%   $244.8328   $244.83   $244.85   $244.80  
  Purchase #3 $40.63   13.222%   $46.0021   $46.00   $46.00   $46.00  
  Purchase #4 $84.70   11.791%   $94.687   $94.69   $94.70   $94.70  
  Purchase #5 $102.65   6.753%   $109.582   $109.58   $109.60   $109.60  
  Purchase #6 $169.36   5.844%   $179.2574   $179.26   $179.25   $179.30  
  Purchase #7 $142.33   12.629%   $160.3049   $160.30   $160.30   $160.30  
  7 purchase totals = $832.16       $918.0439   $918.04   $918.10   $918.10