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	$247.57	4.431%	$258.5398	$258.54	$258.55	$258.50
Purchase #2	$57.76	3.695%	$59.8942	$59.89	$59.90	$59.90
Purchase #3	$171.79	5.702%	$181.5855	$181.59	$181.60	$181.60
Purchase #4	$22.37	4.234%	$23.3171	$23.32	$23.30	$23.30
Purchase #5	$89.38	9.117%	$97.5288	$97.53	$97.55	$97.50
Purchase #6	$120.84	7.109%	$129.4305	$129.43	$129.45	$129.40
Purchase #7	$68.93	13.525%	$78.2528	$78.25	$78.25	$78.30
7 purchase totals =	$778.64		$828.5487	$828.55	$828.60	$828.50