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 $87.47   5.826%   $92.566   $92.57   $92.55   $92.60  
  Purchase #2 $245.38   4.187%   $255.6541   $255.65   $255.65   $255.70  
  Purchase #3 $199.45   8.279%   $215.9625   $215.96   $215.95   $216.00  
  Purchase #4 $26.58   13.548%   $30.1811   $30.18   $30.20   $30.20  
  Purchase #5 $98.77   3.415%   $102.143   $102.14   $102.15   $102.10  
  Purchase #6 $212.90   8.747%   $231.5224   $231.52   $231.50   $231.50  
  Purchase #7 $96.76   3.489%   $100.136   $100.14   $100.15   $100.10  
  7 purchase totals = $967.31       $1,028.1651   $1,028.16   $1,028.15   $1,028.20