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 $39.39   13.257%   $44.6119   $44.61   $44.60   $44.60  
  Purchase #2 $183.31   8.274%   $198.4771   $198.48   $198.50   $198.50  
  Purchase #3 $44.64   13.673%   $50.7436   $50.74   $50.75   $50.70  
  Purchase #4 $209.61   7.159%   $224.616   $224.62   $224.60   $224.60  
  Purchase #5 $143.43   8.357%   $155.4164   $155.42   $155.40   $155.40  
  Purchase #6 $237.37   7.405%   $254.9472   $254.95   $254.95   $254.90  
  Purchase #7 $78.96   5.650%   $83.4212   $83.42   $83.40   $83.40  
  7 purchase totals = $936.71       $1,012.2334   $1,012.24   $1,012.20   $1,012.10