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	$227.43	13.291%	$257.6577	$257.66	$257.65	$257.70
Purchase #2	$174.29	3.807%	$180.9252	$180.93	$180.95	$180.90
Purchase #3	$242.55	12.780%	$273.5479	$273.55	$273.55	$273.50
Purchase #4	$42.63	6.427%	$45.3698	$45.37	$45.35	$45.40
Purchase #5	$84.48	6.810%	$90.2331	$90.23	$90.25	$90.20
Purchase #6	$158.45	4.213%	$165.1255	$165.13	$165.15	$165.10
Purchase #7	$55.43	10.767%	$61.3981	$61.40	$61.40	$61.40
7 purchase totals =	$985.26		$1,074.2573	$1,074.27	$1,074.30	$1,074.20