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 $235.79   13.163%   $266.827   $266.83   $266.85   $266.80  
  Purchase #2 $200.64   11.638%   $223.9905   $223.99   $224.00   $224.00  
  Purchase #3 $200.58   10.565%   $221.7713   $221.77   $221.75   $221.80  
  Purchase #4 $113.82   13.761%   $129.4828   $129.48   $129.50   $129.50  
  Purchase #5 $198.67   5.106%   $208.8141   $208.81   $208.80   $208.80  
  Purchase #6 $244.88   3.848%   $254.303   $254.30   $254.30   $254.30  
  Purchase #7 $56.92   3.332%   $58.8166   $58.82   $58.80   $58.80  
  7 purchase totals = $1,251.30       $1,364.0053   $1,364.00   $1,364.00   $1,364.00