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 $86.37   11.649%   $96.4312   $96.43   $96.45   $96.40  
  Purchase #2 $69.53   11.145%   $77.2791   $77.28   $77.30   $77.30  
  Purchase #3 $33.67   12.719%   $37.9525   $37.95   $37.95   $38.00  
  Purchase #4 $223.31   5.805%   $236.2731   $236.27   $236.25   $236.30  
  Purchase #5 $114.29   8.798%   $124.3452   $124.35   $124.35   $124.30  
  Purchase #6 $231.69   5.453%   $244.3241   $244.32   $244.30   $244.30  
  Purchase #7 $49.45   6.150%   $52.4912   $52.49   $52.50   $52.50  
  7 purchase totals = $808.31       $869.0964   $869.09   $869.10   $869.10