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 $65.86   3.110%   $67.9082   $67.91   $67.90   $67.90  
  Purchase #2 $88.64   4.646%   $92.7582   $92.76   $92.75   $92.80  
  Purchase #3 $240.44   13.223%   $272.2334   $272.23   $272.25   $272.20  
  Purchase #4 $132.79   8.137%   $143.5951   $143.60   $143.60   $143.60  
  Purchase #5 $193.47   5.672%   $204.4436   $204.44   $204.45   $204.40  
  Purchase #6 $19.52   5.784%   $20.649   $20.65   $20.65   $20.60  
  Purchase #7 $185.52   5.641%   $195.9852   $195.99   $196.00   $196.00  
  7 purchase totals = $926.24       $997.5727   $997.58   $997.60   $997.50