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 $136.64   11.311%   $152.0954   $152.10   $152.10   $152.10  
  Purchase #2 $19.34   4.698%   $20.2486   $20.25   $20.25   $20.20  
  Purchase #3 $60.38   9.689%   $66.2302   $66.23   $66.25   $66.20  
  Purchase #4 $186.65   11.638%   $208.3723   $208.37   $208.35   $208.40  
  Purchase #5 $192.52   5.412%   $202.9392   $202.94   $202.95   $202.90  
  Purchase #6 $61.59   7.714%   $66.3411   $66.34   $66.35   $66.30  
  Purchase #7 $227.54   7.371%   $244.312   $244.31   $244.30   $244.30  
  7 purchase totals = $884.66       $960.5388   $960.54   $960.55   $960.40