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 $201.39   5.506%   $212.4785   $212.48   $212.50   $212.50  
  Purchase #2 $106.89   7.548%   $114.9581   $114.96   $114.95   $115.00  
  Purchase #3 $103.99   5.732%   $109.9507   $109.95   $109.95   $110.00  
  Purchase #4 $184.62   8.221%   $199.7976   $199.80   $199.80   $199.80  
  Purchase #5 $96.89   8.582%   $105.2051   $105.21   $105.20   $105.20  
  Purchase #6 $35.96   12.429%   $40.4295   $40.43   $40.45   $40.40  
  Purchase #7 $232.90   4.284%   $242.8774   $242.88   $242.90   $242.90  
  7 purchase totals = $962.64       $1,025.6969   $1,025.71   $1,025.75   $1,025.80