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	$55.59	3.751%	$57.6752	$57.68	$57.70	$57.70
Purchase #2	$66.42	6.760%	$70.91	$70.91	$70.90	$70.90
Purchase #3	$223.51	12.524%	$251.5024	$251.50	$251.50	$251.50
Purchase #4	$92.41	8.464%	$100.2316	$100.23	$100.25	$100.20
Purchase #5	$115.28	6.202%	$122.4297	$122.43	$122.45	$122.40
Purchase #6	$7.35	7.413%	$7.8949	$7.89	$7.90	$7.90
Purchase #7	$244.72	8.124%	$264.6011	$264.60	$264.60	$264.60
7 purchase totals =	$805.28		$875.2449	$875.24	$875.30	$875.20