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 $116.53   5.539%   $122.9846   $122.98   $123.00   $123.00  
  Purchase #2 $93.31   3.832%   $96.8856   $96.89   $96.90   $96.90  
  Purchase #3 $109.42   7.771%   $117.923   $117.92   $117.90   $117.90  
  Purchase #4 $217.26   4.625%   $227.3083   $227.31   $227.30   $227.30  
  Purchase #5 $62.55   13.388%   $70.9242   $70.92   $70.90   $70.90  
  Purchase #6 $80.49   4.486%   $84.1008   $84.10   $84.10   $84.10  
  Purchase #7 $247.48   7.557%   $266.1821   $266.18   $266.20   $266.20  
  7 purchase totals = $927.04       $986.3086   $986.30   $986.30   $986.30