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	$37.85	11.823%	$42.325	$42.33	$42.35	$42.30
Purchase #2	$189.57	11.152%	$210.7108	$210.71	$210.70	$210.70
Purchase #3	$90.55	12.347%	$101.7302	$101.73	$101.75	$101.70
Purchase #4	$197.99	12.160%	$222.0656	$222.07	$222.05	$222.10
Purchase #5	$222.41	10.379%	$245.4939	$245.49	$245.50	$245.50
Purchase #6	$246.56	3.227%	$254.5165	$254.52	$254.50	$254.50
Purchase #7	$161.52	10.753%	$178.8882	$178.89	$178.90	$178.90
7 purchase totals =	$1,146.45		$1,255.7302	$1,255.74	$1,255.75	$1,255.70