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 $245.53   7.624%   $264.2492   $264.25   $264.25   $264.20  
  Purchase #2 $247.73   9.771%   $271.9357   $271.94   $271.95   $271.90  
  Purchase #3 $17.61   10.254%   $19.4157   $19.42   $19.40   $19.40  
  Purchase #4 $22.77   9.570%   $24.9491   $24.95   $24.95   $24.90  
  Purchase #5 $242.50   6.258%   $257.6757   $257.68   $257.70   $257.70  
  Purchase #6 $31.61   9.282%   $34.544   $34.54   $34.55   $34.50  
  Purchase #7 $16.66   10.192%   $18.358   $18.36   $18.35   $18.40  
  7 purchase totals = $824.41       $891.1274   $891.14   $891.15   $891.00