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 $233.78   13.182%   $264.5969   $264.60   $264.60   $264.60  
  Purchase #2 $195.97   9.151%   $213.9032   $213.90   $213.90   $213.90  
  Purchase #3 $192.97   5.415%   $203.4193   $203.42   $203.40   $203.40  
  Purchase #4 $239.43   7.547%   $257.4998   $257.50   $257.50   $257.50  
  Purchase #5 $86.26   12.435%   $96.9864   $96.99   $97.00   $97.00  
  Purchase #6 $49.58   5.143%   $52.1299   $52.13   $52.15   $52.10  
  Purchase #7 $94.62   13.266%   $107.1723   $107.17   $107.15   $107.20  
  7 purchase totals = $1,092.61       $1,195.7078   $1,195.71   $1,195.70   $1,195.70