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	$243.36	13.318%	$275.7707	$275.77	$275.75	$275.80
Purchase #2	$20.60	6.211%	$21.8795	$21.88	$21.90	$21.90
Purchase #3	$74.74	5.674%	$78.9807	$78.98	$79.00	$79.00
Purchase #4	$144.34	10.271%	$159.1652	$159.17	$159.15	$159.20
Purchase #5	$202.85	9.677%	$222.4798	$222.48	$222.50	$222.50
Purchase #6	$45.83	10.276%	$50.5395	$50.54	$50.55	$50.50
Purchase #7	$218.39	10.694%	$241.7446	$241.74	$241.75	$241.70
7 purchase totals =	$950.11		$1,050.5600	$1,050.56	$1,050.60	$1,050.60