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 $110.72   13.783%   $125.9805   $125.98   $126.00   $126.00  
  Purchase #2 $24.55   9.145%   $26.7951   $26.80   $26.80   $26.80  
  Purchase #3 $241.58   10.222%   $266.2743   $266.27   $266.25   $266.30  
  Purchase #4 $137.94   7.131%   $147.7765   $147.78   $147.80   $147.80  
  Purchase #5 $221.84   9.673%   $243.2986   $243.30   $243.30   $243.30  
  Purchase #6 $94.81   7.377%   $101.8041   $101.80   $101.80   $101.80  
  Purchase #7 $22.86   4.486%   $23.8855   $23.89   $23.90   $23.90  
  7 purchase totals = $854.30       $935.8146   $935.82   $935.85   $935.90