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 $210.71   10.622%   $233.0916   $233.09   $233.10   $233.10  
  Purchase #2 $32.85   12.404%   $36.9247   $36.92   $36.90   $36.90  
  Purchase #3 $48.54   12.398%   $54.558   $54.56   $54.55   $54.60  
  Purchase #4 $73.86   6.266%   $78.4881   $78.49   $78.50   $78.50  
  Purchase #5 $114.50   9.782%   $125.7004   $125.70   $125.70   $125.70  
  Purchase #6 $5.49   8.765%   $5.9712   $5.97   $5.95   $6.00  
  Purchase #7 $68.73   7.236%   $73.7033   $73.70   $73.70   $73.70  
  7 purchase totals = $554.68       $608.4373   $608.43   $608.40   $608.50