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 $246.74   4.341%   $257.451   $257.45   $257.45   $257.50  
  Purchase #2 $67.45   7.822%   $72.7259   $72.73   $72.75   $72.70  
  Purchase #3 $10.50   11.517%   $11.7093   $11.71   $11.70   $11.70  
  Purchase #4 $167.77   8.498%   $182.0271   $182.03   $182.05   $182.00  
  Purchase #5 $225.46   11.658%   $251.7441   $251.74   $251.75   $251.70  
  Purchase #6 $60.93   9.305%   $66.5995   $66.60   $66.60   $66.60  
  Purchase #7 $210.47   9.686%   $230.8561   $230.86   $230.85   $230.90  
  7 purchase totals = $989.32       $1,073.1130   $1,073.12   $1,073.15   $1,073.10