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	$133.45	11.501%	$148.7981	$148.80	$148.80	$148.80
Purchase #2	$31.29	3.820%	$32.4853	$32.49	$32.50	$32.50
Purchase #3	$243.95	10.185%	$268.7963	$268.80	$268.80	$268.80
Purchase #4	$181.71	11.824%	$203.1954	$203.20	$203.20	$203.20
Purchase #5	$67.55	4.794%	$70.7883	$70.79	$70.80	$70.80
Purchase #6	$45.72	10.700%	$50.612	$50.61	$50.60	$50.60
Purchase #7	$134.56	9.181%	$146.914	$146.91	$146.90	$146.90
7 purchase totals =	$838.23		$921.5894	$921.60	$921.60	$921.60