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 $119.94   8.639%   $130.3016   $130.30   $130.30   $130.30  
  Purchase #2 $61.38   6.793%   $65.5495   $65.55   $65.55   $65.50  
  Purchase #3 $29.50   4.633%   $30.8667   $30.87   $30.85   $30.90  
  Purchase #4 $230.89   8.709%   $250.9982   $251.00   $251.00   $251.00  
  Purchase #5 $127.64   5.866%   $135.1274   $135.13   $135.15   $135.10  
  Purchase #6 $162.74   5.383%   $171.5003   $171.50   $171.50   $171.50  
  Purchase #7 $205.49   3.802%   $213.3027   $213.30   $213.30   $213.30  
  7 purchase totals = $937.58       $997.6464   $997.65   $997.65   $997.60