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	$66.62	10.120%	$73.3619	$73.36	$73.35	$73.40
Purchase #2	$162.84	5.468%	$171.7441	$171.74	$171.75	$171.70
Purchase #3	$169.89	12.360%	$190.8884	$190.89	$190.90	$190.90
Purchase #4	$244.75	4.204%	$255.0393	$255.04	$255.05	$255.00
Purchase #5	$42.33	10.353%	$46.7124	$46.71	$46.70	$46.70
Purchase #6	$247.66	9.855%	$272.0669	$272.07	$272.05	$272.10
Purchase #7	$65.91	6.663%	$70.3016	$70.30	$70.30	$70.30
7 purchase totals =	$1,000.00		$1,080.1146	$1,080.11	$1,080.10	$1,080.10