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 $195.86   3.631%   $202.9717   $202.97   $202.95   $203.00  
  Purchase #2 $49.89   4.208%   $51.9894   $51.99   $52.00   $52.00  
  Purchase #3 $225.71   7.659%   $242.9971   $243.00   $243.00   $243.00  
  Purchase #4 $162.39   6.221%   $172.4923   $172.49   $172.50   $172.50  
  Purchase #5 $100.63   10.398%   $111.0935   $111.09   $111.10   $111.10  
  Purchase #6 $238.41   13.209%   $269.9016   $269.90   $269.90   $269.90  
  Purchase #7 $12.46   12.315%   $13.9944   $13.99   $14.00   $14.00  
  7 purchase totals = $985.35       $1,065.4400   $1,065.43   $1,065.45   $1,065.50