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 $68.43   7.693%   $73.6943   $73.69   $73.70   $73.70  
  Purchase #2 $74.27   7.249%   $79.6538   $79.65   $79.65   $79.70  
  Purchase #3 $238.29   4.745%   $249.5969   $249.60   $249.60   $249.60  
  Purchase #4 $247.29   5.269%   $260.3197   $260.32   $260.30   $260.30  
  Purchase #5 $175.25   9.679%   $192.2124   $192.21   $192.20   $192.20  
  Purchase #6 $229.48   13.719%   $260.9624   $260.96   $260.95   $261.00  
  Purchase #7 $98.74   4.684%   $103.365   $103.37   $103.35   $103.40  
  7 purchase totals = $1,131.75       $1,219.8045   $1,219.80   $1,219.75   $1,219.90