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 $173.95   11.145%   $193.3367   $193.34   $193.35   $193.30  
  Purchase #2 $135.64   9.136%   $148.0321   $148.03   $148.05   $148.00  
  Purchase #3 $22.45   8.441%   $24.345   $24.35   $24.35   $24.30  
  Purchase #4 $137.29   7.858%   $148.0782   $148.08   $148.10   $148.10  
  Purchase #5 $94.38   11.103%   $104.859   $104.86   $104.85   $104.90  
  Purchase #6 $90.46   6.802%   $96.6131   $96.61   $96.60   $96.60  
  Purchase #7 $37.54   6.853%   $40.1126   $40.11   $40.10   $40.10  
  7 purchase totals = $691.71       $755.3767   $755.38   $755.40   $755.30