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 $54.95   9.293%   $60.0565   $60.06   $60.05   $60.10  
  Purchase #2 $25.99   10.549%   $28.7317   $28.73   $28.75   $28.70  
  Purchase #3 $124.28   13.295%   $140.803   $140.80   $140.80   $140.80  
  Purchase #4 $128.90   3.667%   $133.6268   $133.63   $133.65   $133.60  
  Purchase #5 $201.71   9.519%   $220.9108   $220.91   $220.90   $220.90  
  Purchase #6 $85.97   3.328%   $88.8311   $88.83   $88.85   $88.80  
  Purchase #7 $225.49   3.660%   $233.7429   $233.74   $233.75   $233.70  
  7 purchase totals = $847.29       $906.7028   $906.70   $906.75   $906.60