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	$137.99	10.571%	$152.5769	$152.58	$152.60	$152.60
Purchase #2	$177.31	9.747%	$194.5924	$194.59	$194.60	$194.60
Purchase #3	$212.34	12.104%	$238.0416	$238.04	$238.05	$238.00
Purchase #4	$16.62	9.811%	$18.2506	$18.25	$18.25	$18.30
Purchase #5	$134.70	13.366%	$152.704	$152.70	$152.70	$152.70
Purchase #6	$166.89	13.759%	$189.8524	$189.85	$189.85	$189.90
Purchase #7	$38.53	10.190%	$42.4562	$42.46	$42.45	$42.50
7 purchase totals =	$884.38		$988.4741	$988.47	$988.50	$988.60