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 $60.50   7.292%   $64.9117   $64.91   $64.90   $64.90  
  Purchase #2 $215.41   8.746%   $234.2498   $234.25   $234.25   $234.20  
  Purchase #3 $53.70   4.104%   $55.9038   $55.90   $55.90   $55.90  
  Purchase #4 $233.96   11.444%   $260.7344   $260.73   $260.75   $260.70  
  Purchase #5 $55.80   8.512%   $60.5497   $60.55   $60.55   $60.50  
  Purchase #6 $23.39   4.132%   $24.3565   $24.36   $24.35   $24.40  
  Purchase #7 $58.66   5.597%   $61.9432   $61.94   $61.95   $61.90  
  7 purchase totals = $701.42       $762.6491   $762.64   $762.65   $762.50