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 $122.84   3.152%   $126.7119   $126.71   $126.70   $126.70  
  Purchase #2 $181.43   12.212%   $203.5862   $203.59   $203.60   $203.60  
  Purchase #3 $69.50   3.462%   $71.9061   $71.91   $71.90   $71.90  
  Purchase #4 $245.71   6.420%   $261.4846   $261.48   $261.50   $261.50  
  Purchase #5 $67.43   10.403%   $74.4447   $74.44   $74.45   $74.40  
  Purchase #6 $22.61   8.742%   $24.5866   $24.59   $24.60   $24.60  
  Purchase #7 $31.76   3.181%   $32.7703   $32.77   $32.75   $32.80  
  7 purchase totals = $741.28       $795.4904   $795.49   $795.50   $795.50