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	$250.37	10.128%	$275.7275	$275.73	$275.75	$275.70
Purchase #2	$72.80	10.869%	$80.7126	$80.71	$80.70	$80.70
Purchase #3	$169.62	7.271%	$181.9531	$181.95	$181.95	$182.00
Purchase #4	$87.80	13.807%	$99.9225	$99.92	$99.90	$99.90
Purchase #5	$37.77	6.670%	$40.2893	$40.29	$40.30	$40.30
Purchase #6	$50.26	8.583%	$54.5738	$54.57	$54.55	$54.60
Purchase #7	$212.57	4.537%	$222.2143	$222.21	$222.20	$222.20
7 purchase totals =	$881.19		$955.3931	$955.38	$955.35	$955.40