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 $121.28   4.723%   $127.0081   $127.01   $127.00   $127.00  
  Purchase #2 $87.61   6.587%   $93.3809   $93.38   $93.40   $93.40  
  Purchase #3 $51.44   5.589%   $54.315   $54.32   $54.30   $54.30  
  Purchase #4 $83.84   6.508%   $89.2963   $89.30   $89.30   $89.30  
  Purchase #5 $130.67   10.128%   $143.9043   $143.90   $143.90   $143.90  
  Purchase #6 $243.73   10.167%   $268.51   $268.51   $268.50   $268.50  
  Purchase #7 $64.58   5.812%   $68.3334   $68.33   $68.35   $68.30  
  7 purchase totals = $783.15       $844.7480   $844.75   $844.75   $844.70