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 $26.32   5.407%   $27.7431   $27.74   $27.75   $27.70  
  Purchase #2 $204.97   7.701%   $220.7547   $220.75   $220.75   $220.80  
  Purchase #3 $79.49   5.800%   $84.1004   $84.10   $84.10   $84.10  
  Purchase #4 $214.74   8.563%   $233.1282   $233.13   $233.15   $233.10  
  Purchase #5 $123.79   8.546%   $134.3691   $134.37   $134.35   $134.40  
  Purchase #6 $72.80   12.365%   $81.8017   $81.80   $81.80   $81.80  
  Purchase #7 $5.95   10.389%   $6.5681   $6.57   $6.55   $6.60  
  7 purchase totals = $728.06       $788.4653   $788.46   $788.45   $788.50