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 $237.87   10.754%   $263.4505   $263.45   $263.45   $263.50  
  Purchase #2 $122.52   3.219%   $126.4639   $126.46   $126.45   $126.50  
  Purchase #3 $213.57   3.280%   $220.5751   $220.58   $220.60   $220.60  
  Purchase #4 $224.34   11.430%   $249.9821   $249.98   $250.00   $250.00  
  Purchase #5 $238.78   10.831%   $264.6423   $264.64   $264.65   $264.60  
  Purchase #6 $173.81   5.240%   $182.9176   $182.92   $182.90   $182.90  
  Purchase #7 $70.36   8.659%   $76.4525   $76.45   $76.45   $76.50  
  7 purchase totals = $1,281.25       $1,384.4840   $1,384.48   $1,384.50   $1,384.60