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	$166.56	3.552%	$172.4762	$172.48	$172.50	$172.50
Purchase #2	$245.55	12.327%	$275.8189	$275.82	$275.80	$275.80
Purchase #3	$39.79	7.696%	$42.8522	$42.85	$42.85	$42.90
Purchase #4	$200.25	5.869%	$212.0027	$212.00	$212.00	$212.00
Purchase #5	$242.77	13.819%	$276.3184	$276.32	$276.30	$276.30
Purchase #6	$181.32	10.698%	$200.7176	$200.72	$200.70	$200.70
Purchase #7	$12.26	10.477%	$13.5445	$13.54	$13.55	$13.50
7 purchase totals =	$1,088.50		$1,193.7305	$1,193.73	$1,193.70	$1,193.70