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 $52.45   5.866%   $55.5267   $55.53   $55.55   $55.50  
  Purchase #2 $138.97   6.134%   $147.4944   $147.49   $147.50   $147.50  
  Purchase #3 $24.60   5.410%   $25.9309   $25.93   $25.95   $25.90  
  Purchase #4 $202.28   7.577%   $217.6068   $217.61   $217.60   $217.60  
  Purchase #5 $186.73   4.679%   $195.4671   $195.47   $195.45   $195.50  
  Purchase #6 $73.40   10.518%   $81.1202   $81.12   $81.10   $81.10  
  Purchase #7 $62.42   4.460%   $65.2039   $65.20   $65.20   $65.20  
  7 purchase totals = $740.85       $788.3500   $788.35   $788.35   $788.30