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	$31.78	4.401%	$33.1786	$33.18	$33.20	$33.20
Purchase #2	$54.31	6.634%	$57.9129	$57.91	$57.90	$57.90
Purchase #3	$35.78	8.478%	$38.8134	$38.81	$38.80	$38.80
Purchase #4	$40.33	13.358%	$45.7173	$45.72	$45.70	$45.70
Purchase #5	$70.85	8.330%	$76.7518	$76.75	$76.75	$76.80
Purchase #6	$144.88	7.263%	$155.4026	$155.40	$155.40	$155.40
Purchase #7	$51.97	9.203%	$56.7528	$56.75	$56.75	$56.80
7 purchase totals =	$429.90		$464.5294	$464.52	$464.50	$464.60