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	$97.32	4.174%	$101.3821	$101.38	$101.40	$101.40
Purchase #2	$235.86	12.116%	$264.4368	$264.44	$264.45	$264.40
Purchase #3	$54.64	12.820%	$61.6448	$61.64	$61.65	$61.60
Purchase #4	$206.29	3.331%	$213.1615	$213.16	$213.15	$213.20
Purchase #5	$247.33	11.322%	$275.3327	$275.33	$275.35	$275.30
Purchase #6	$78.89	12.199%	$88.5138	$88.51	$88.50	$88.50
Purchase #7	$232.53	8.855%	$253.1205	$253.12	$253.10	$253.10
7 purchase totals =	$1,152.86		$1,257.5922	$1,257.58	$1,257.60	$1,257.50