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 $60.83   10.120%   $66.986   $66.99   $67.00   $67.00  
  Purchase #2 $181.52   6.602%   $193.504   $193.50   $193.50   $193.50  
  Purchase #3 $66.63   9.838%   $73.1851   $73.19   $73.20   $73.20  
  Purchase #4 $153.28   6.781%   $163.6739   $163.67   $163.65   $163.70  
  Purchase #5 $12.78   3.622%   $13.2429   $13.24   $13.25   $13.20  
  Purchase #6 $160.93   12.461%   $180.9835   $180.98   $181.00   $181.00  
  Purchase #7 $148.97   7.484%   $160.1189   $160.12   $160.10   $160.10  
  7 purchase totals = $784.94       $851.6943   $851.69   $851.70   $851.70