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	$69.86	3.231%	$72.1172	$72.12	$72.10	$72.10
Purchase #2	$28.40	4.780%	$29.7575	$29.76	$29.75	$29.80
Purchase #3	$111.73	12.668%	$125.884	$125.88	$125.90	$125.90
Purchase #4	$180.86	8.767%	$196.716	$196.72	$196.70	$196.70
Purchase #5	$173.26	3.764%	$179.7815	$179.78	$179.80	$179.80
Purchase #6	$31.29	10.684%	$34.633	$34.63	$34.65	$34.60
Purchase #7	$10.45	7.468%	$11.2304	$11.23	$11.25	$11.20
7 purchase totals =	$605.85		$650.1196	$650.12	$650.15	$650.10