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 $67.53   13.635%   $76.7377   $76.74   $76.75   $76.70  
  Purchase #2 $214.57   4.553%   $224.3394   $224.34   $224.35   $224.30  
  Purchase #3 $158.79   4.436%   $165.8339   $165.83   $165.85   $165.80  
  Purchase #4 $202.75   11.214%   $225.4864   $225.49   $225.50   $225.50  
  Purchase #5 $180.66   6.741%   $192.8383   $192.84   $192.85   $192.80  
  Purchase #6 $226.61   13.482%   $257.1616   $257.16   $257.15   $257.20  
  Purchase #7 $92.62   13.330%   $104.9662   $104.97   $104.95   $105.00  
  7 purchase totals = $1,143.53       $1,247.3635   $1,247.37   $1,247.40   $1,247.30