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	$10.83	12.840%	$12.2206	$12.22	$12.20	$12.20
Purchase #2	$78.84	13.525%	$89.5031	$89.50	$89.50	$89.50
Purchase #3	$150.32	10.722%	$166.4373	$166.44	$166.45	$166.40
Purchase #4	$109.90	6.410%	$116.9446	$116.94	$116.95	$116.90
Purchase #5	$221.83	3.515%	$229.6273	$229.63	$229.65	$229.60
Purchase #6	$172.62	5.120%	$181.4581	$181.46	$181.45	$181.50
Purchase #7	$78.91	7.127%	$84.5339	$84.53	$84.55	$84.50
7 purchase totals =	$823.25		$880.7249	$880.72	$880.75	$880.60