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 $164.56   13.172%   $186.2358   $186.24   $186.25   $186.20  
  Purchase #2 $49.97   6.602%   $53.269   $53.27   $53.25   $53.30  
  Purchase #3 $29.28   12.850%   $33.0425   $33.04   $33.05   $33.00  
  Purchase #4 $195.93   10.647%   $216.7907   $216.79   $216.80   $216.80  
  Purchase #5 $125.51   5.759%   $132.7381   $132.74   $132.75   $132.70  
  Purchase #6 $53.91   13.290%   $61.0746   $61.07   $61.05   $61.10  
  Purchase #7 $244.94   5.784%   $259.1073   $259.11   $259.10   $259.10  
  7 purchase totals = $864.10       $942.2580   $942.26   $942.25   $942.20