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 $207.94   6.426%   $221.3022   $221.30   $221.30   $221.30  
  Purchase #2 $116.35   8.727%   $126.5039   $126.50   $126.50   $126.50  
  Purchase #3 $188.38   4.624%   $197.0907   $197.09   $197.10   $197.10  
  Purchase #4 $40.48   12.583%   $45.5736   $45.57   $45.55   $45.60  
  Purchase #5 $33.28   9.558%   $36.4609   $36.46   $36.45   $36.50  
  Purchase #6 $105.82   11.477%   $117.965   $117.97   $117.95   $118.00  
  Purchase #7 $234.93   5.288%   $247.3531   $247.35   $247.35   $247.40  
  7 purchase totals = $927.18       $992.2494   $992.24   $992.20   $992.40