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 $185.94   8.273%   $201.3228   $201.32   $201.30   $201.30  
  Purchase #2 $209.26   11.132%   $232.5548   $232.55   $232.55   $232.60  
  Purchase #3 $42.55   6.649%   $45.3791   $45.38   $45.40   $45.40  
  Purchase #4 $92.98   3.163%   $95.921   $95.92   $95.90   $95.90  
  Purchase #5 $148.75   10.320%   $164.101   $164.10   $164.10   $164.10  
  Purchase #6 $20.40   11.431%   $22.7319   $22.73   $22.75   $22.70  
  Purchase #7 $90.78   5.550%   $95.8183   $95.82   $95.80   $95.80  
  7 purchase totals = $790.66       $857.8289   $857.82   $857.80   $857.80