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	$48.53	9.649%	$53.2127	$53.21	$53.20	$53.20
Purchase #2	$235.28	3.836%	$244.3053	$244.31	$244.30	$244.30
Purchase #3	$146.50	10.607%	$162.0393	$162.04	$162.05	$162.00
Purchase #4	$73.56	12.342%	$82.6388	$82.64	$82.65	$82.60
Purchase #5	$48.94	7.662%	$52.6898	$52.69	$52.70	$52.70
Purchase #6	$62.26	7.522%	$66.9432	$66.94	$66.95	$66.90
Purchase #7	$248.88	8.443%	$269.8929	$269.89	$269.90	$269.90
7 purchase totals =	$863.95		$931.7220	$931.72	$931.75	$931.60