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 $84.65   10.187%   $93.2733   $93.27   $93.25   $93.30  
  Purchase #2 $232.52   13.230%   $263.2824   $263.28   $263.30   $263.30  
  Purchase #3 $183.58   10.533%   $202.9165   $202.92   $202.90   $202.90  
  Purchase #4 $214.85   10.567%   $237.5532   $237.55   $237.55   $237.60  
  Purchase #5 $73.92   12.827%   $83.4017   $83.40   $83.40   $83.40  
  Purchase #6 $68.87   9.267%   $75.2522   $75.25   $75.25   $75.30  
  Purchase #7 $185.57   4.748%   $194.3809   $194.38   $194.40   $194.40  
  7 purchase totals = $1,043.96       $1,150.0602   $1,150.05   $1,150.05   $1,150.20