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	$120.54	3.278%	$124.4913	$124.49	$124.50	$124.50
Purchase #2	$79.75	13.356%	$90.4014	$90.40	$90.40	$90.40
Purchase #3	$122.44	7.485%	$131.6046	$131.60	$131.60	$131.60
Purchase #4	$64.34	11.288%	$71.6027	$71.60	$71.60	$71.60
Purchase #5	$188.74	11.873%	$211.1491	$211.15	$211.15	$211.10
Purchase #6	$30.95	8.269%	$33.5093	$33.51	$33.50	$33.50
Purchase #7	$55.51	6.647%	$59.1997	$59.20	$59.20	$59.20
7 purchase totals =	$662.27		$721.9581	$721.95	$721.95	$721.90