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 $247.36   13.683%   $281.2063   $281.21   $281.20   $281.20  
  Purchase #2 $28.41   8.357%   $30.7842   $30.78   $30.80   $30.80  
  Purchase #3 $61.67   10.516%   $68.1552   $68.16   $68.15   $68.20  
  Purchase #4 $223.67   6.244%   $237.636   $237.64   $237.65   $237.60  
  Purchase #5 $212.81   13.659%   $241.8777   $241.88   $241.90   $241.90  
  Purchase #6 $132.99   8.451%   $144.229   $144.23   $144.25   $144.20  
  Purchase #7 $129.86   11.483%   $144.7718   $144.77   $144.75   $144.80  
  7 purchase totals = $1,036.77       $1,148.6602   $1,148.67   $1,148.70   $1,148.70