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 $62.48   13.140%   $70.6899   $70.69   $70.70   $70.70  
  Purchase #2 $27.36   3.322%   $28.2689   $28.27   $28.25   $28.30  
  Purchase #3 $198.65   10.219%   $218.95   $218.95   $218.95   $219.00  
  Purchase #4 $119.98   13.257%   $135.8857   $135.89   $135.90   $135.90  
  Purchase #5 $74.86   4.455%   $78.195   $78.20   $78.20   $78.20  
  Purchase #6 $118.83   4.542%   $124.2273   $124.23   $124.25   $124.20  
  Purchase #7 $223.97   10.463%   $247.404   $247.40   $247.40   $247.40  
  7 purchase totals = $826.13       $903.6208   $903.63   $903.65   $903.70