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	$25.78	11.515%	$28.7486	$28.75	$28.75	$28.70
Purchase #2	$160.86	6.386%	$171.1325	$171.13	$171.15	$171.10
Purchase #3	$242.28	3.869%	$251.6538	$251.65	$251.65	$251.70
Purchase #4	$84.70	12.667%	$95.4289	$95.43	$95.45	$95.40
Purchase #5	$211.56	6.272%	$224.829	$224.83	$224.85	$224.80
Purchase #6	$246.31	7.255%	$264.1798	$264.18	$264.20	$264.20
Purchase #7	$55.77	6.727%	$59.5216	$59.52	$59.50	$59.50
7 purchase totals =	$1,027.26		$1,095.4942	$1,095.49	$1,095.55	$1,095.40