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 $242.35   10.174%   $267.0067   $267.01   $267.00   $267.00  
  Purchase #2 $55.60   13.533%   $63.1243   $63.12   $63.10   $63.10  
  Purchase #3 $6.95   10.813%   $7.7015   $7.70   $7.70   $7.70  
  Purchase #4 $109.57   5.848%   $115.9777   $115.98   $116.00   $116.00  
  Purchase #5 $180.36   10.661%   $199.5882   $199.59   $199.60   $199.60  
  Purchase #6 $131.33   11.161%   $145.9877   $145.99   $146.00   $146.00  
  Purchase #7 $210.77   12.785%   $237.7169   $237.72   $237.70   $237.70  
  7 purchase totals = $936.93       $1,037.1030   $1,037.11   $1,037.10   $1,037.10