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 $68.99   9.269%   $75.3847   $75.38   $75.40   $75.40  
  Purchase #2 $245.41   11.586%   $273.8432   $273.84   $273.85   $273.80  
  Purchase #3 $93.66   11.239%   $104.1864   $104.19   $104.20   $104.20  
  Purchase #4 $206.42   4.669%   $216.0577   $216.06   $216.05   $216.10  
  Purchase #5 $232.51   4.578%   $243.1543   $243.15   $243.15   $243.20  
  Purchase #6 $159.46   10.587%   $176.342   $176.34   $176.35   $176.30  
  Purchase #7 $104.58   13.376%   $118.5686   $118.57   $118.55   $118.60  
  7 purchase totals = $1,111.03       $1,207.5369   $1,207.53   $1,207.55   $1,207.60