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 $69.73   8.771%   $75.846   $75.85   $75.85   $75.80  
  Purchase #2 $80.36   5.467%   $84.7533   $84.75   $84.75   $84.80  
  Purchase #3 $51.42   13.686%   $58.4573   $58.46   $58.45   $58.50  
  Purchase #4 $71.59   6.417%   $76.1839   $76.18   $76.20   $76.20  
  Purchase #5 $81.93   3.154%   $84.5141   $84.51   $84.50   $84.50  
  Purchase #6 $129.69   13.127%   $146.7144   $146.71   $146.70   $146.70  
  Purchase #7 $42.85   11.368%   $47.7212   $47.72   $47.70   $47.70  
  7 purchase totals = $527.57       $574.1902   $574.18   $574.15   $574.20