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 $86.67   9.184%   $94.6298   $94.63   $94.65   $94.60  
  Purchase #2 $99.58   9.218%   $108.7593   $108.76   $108.75   $108.80  
  Purchase #3 $107.61   9.350%   $117.6715   $117.67   $117.65   $117.70  
  Purchase #4 $45.38   7.566%   $48.8135   $48.81   $48.80   $48.80  
  Purchase #5 $45.65   9.654%   $50.0571   $50.06   $50.05   $50.10  
  Purchase #6 $113.73   5.204%   $119.6485   $119.65   $119.65   $119.60  
  Purchase #7 $207.83   6.298%   $220.9191   $220.92   $220.90   $220.90  
  7 purchase totals = $706.45       $760.4988   $760.50   $760.45   $760.50