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 $50.64   11.246%   $56.335   $56.34   $56.35   $56.30  
  Purchase #2 $169.43   9.777%   $185.9952   $186.00   $186.00   $186.00  
  Purchase #3 $159.32   13.538%   $180.8887   $180.89   $180.90   $180.90  
  Purchase #4 $124.74   9.412%   $136.4805   $136.48   $136.50   $136.50  
  Purchase #5 $203.25   6.246%   $215.945   $215.95   $215.95   $215.90  
  Purchase #6 $144.65   11.111%   $160.7221   $160.72   $160.70   $160.70  
  Purchase #7 $43.36   13.665%   $49.2851   $49.29   $49.30   $49.30  
  7 purchase totals = $895.39       $985.6516   $985.67   $985.70   $985.60