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 $228.26   13.747%   $259.6389   $259.64   $259.65   $259.60  
  Purchase #2 $128.33   8.512%   $139.2534   $139.25   $139.25   $139.30  
  Purchase #3 $7.50   7.618%   $8.0714   $8.07   $8.05   $8.10  
  Purchase #4 $32.52   11.185%   $36.1574   $36.16   $36.15   $36.20  
  Purchase #5 $60.77   5.608%   $64.178   $64.18   $64.20   $64.20  
  Purchase #6 $157.53   8.122%   $170.3246   $170.32   $170.30   $170.30  
  Purchase #7 $80.95   3.632%   $83.8901   $83.89   $83.90   $83.90  
  7 purchase totals = $695.86       $761.5138   $761.51   $761.50   $761.60