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	$237.34	7.482%	$255.0978	$255.10	$255.10	$255.10
Purchase #2	$48.80	12.396%	$54.8492	$54.85	$54.85	$54.80
Purchase #3	$222.30	11.258%	$247.3265	$247.33	$247.35	$247.30
Purchase #4	$223.56	12.182%	$250.7941	$250.79	$250.80	$250.80
Purchase #5	$191.75	4.492%	$200.3634	$200.36	$200.35	$200.40
Purchase #6	$85.25	5.166%	$89.654	$89.65	$89.65	$89.70
Purchase #7	$165.39	5.631%	$174.7031	$174.70	$174.70	$174.70
7 purchase totals =	$1,174.39		$1,272.7881	$1,272.78	$1,272.80	$1,272.80