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	$159.27	13.512%	$180.7906	$180.79	$180.80	$180.80
Purchase #2	$95.39	5.580%	$100.7128	$100.71	$100.70	$100.70
Purchase #3	$114.79	4.599%	$120.0692	$120.07	$120.05	$120.10
Purchase #4	$128.88	7.483%	$138.5241	$138.52	$138.50	$138.50
Purchase #5	$231.54	10.109%	$254.9464	$254.95	$254.95	$254.90
Purchase #6	$80.89	10.309%	$89.229	$89.23	$89.25	$89.20
Purchase #7	$174.58	12.710%	$196.7691	$196.77	$196.75	$196.80
7 purchase totals =	$985.34		$1,081.0412	$1,081.04	$1,081.00	$1,081.00