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 $103.48   9.707%   $113.5248   $113.52   $113.50   $113.50  
  Purchase #2 $41.66   4.684%   $43.6114   $43.61   $43.60   $43.60  
  Purchase #3 $70.65   8.346%   $76.5464   $76.55   $76.55   $76.50  
  Purchase #4 $110.37   6.581%   $117.6334   $117.63   $117.65   $117.60  
  Purchase #5 $109.99   7.754%   $118.5186   $118.52   $118.50   $118.50  
  Purchase #6 $96.85   4.400%   $101.1114   $101.11   $101.10   $101.10  
  Purchase #7 $124.51   12.591%   $140.1871   $140.19   $140.20   $140.20  
  7 purchase totals = $657.51       $711.1331   $711.13   $711.10   $711.00