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	$86.92	3.265%	$89.7579	$89.76	$89.75	$89.80
Purchase #2	$110.78	12.529%	$124.6596	$124.66	$124.65	$124.70
Purchase #3	$63.31	6.277%	$67.284	$67.28	$67.30	$67.30
Purchase #4	$47.45	4.714%	$49.6868	$49.69	$49.70	$49.70
Purchase #5	$141.30	6.393%	$150.3333	$150.33	$150.35	$150.30
Purchase #6	$84.41	6.224%	$89.6637	$89.66	$89.65	$89.70
Purchase #7	$176.43	11.556%	$196.8183	$196.82	$196.80	$196.80
7 purchase totals =	$710.60		$768.2036	$768.20	$768.20	$768.30