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 $76.71   6.522%   $81.713   $81.71   $81.70   $81.70  
  Purchase #2 $113.51   8.367%   $123.0074   $123.01   $123.00   $123.00  
  Purchase #3 $21.88   5.301%   $23.0399   $23.04   $23.05   $23.00  
  Purchase #4 $115.95   8.219%   $125.4799   $125.48   $125.50   $125.50  
  Purchase #5 $89.96   7.672%   $96.8617   $96.86   $96.85   $96.90  
  Purchase #6 $144.31   7.240%   $154.758   $154.76   $154.75   $154.80  
  Purchase #7 $191.42   5.174%   $201.3241   $201.32   $201.30   $201.30  
  7 purchase totals = $753.74       $806.1840   $806.18   $806.15   $806.20