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	$71.76	10.434%	$79.2474	$79.25	$79.25	$79.20
Purchase #2	$71.33	8.216%	$77.1905	$77.19	$77.20	$77.20
Purchase #3	$51.45	9.648%	$56.4139	$56.41	$56.40	$56.40
Purchase #4	$115.57	13.553%	$131.2332	$131.23	$131.25	$131.20
Purchase #5	$17.56	7.869%	$18.9418	$18.94	$18.95	$18.90
Purchase #6	$56.67	3.814%	$58.8314	$58.83	$58.85	$58.80
Purchase #7	$103.86	6.700%	$110.8186	$110.82	$110.80	$110.80
7 purchase totals =	$488.20		$532.6768	$532.67	$532.70	$532.50