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 $39.68   3.714%   $41.1537   $41.15   $41.15   $41.20  
  Purchase #2 $245.54   5.604%   $259.3001   $259.30   $259.30   $259.30  
  Purchase #3 $70.98   5.117%   $74.612   $74.61   $74.60   $74.60  
  Purchase #4 $92.39   7.254%   $99.092   $99.09   $99.10   $99.10  
  Purchase #5 $118.85   7.297%   $127.5225   $127.52   $127.50   $127.50  
  Purchase #6 $51.54   10.466%   $56.9342   $56.93   $56.95   $56.90  
  Purchase #7 $85.85   13.432%   $97.3814   $97.38   $97.40   $97.40  
  7 purchase totals = $704.83       $755.9959   $755.98   $756.00   $756.00