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	$130.81	4.486%	$136.6781	$136.68	$136.70	$136.70
Purchase #2	$36.45	12.513%	$41.011	$41.01	$41.00	$41.00
Purchase #3	$51.40	12.614%	$57.8836	$57.88	$57.90	$57.90
Purchase #4	$88.76	9.457%	$97.154	$97.15	$97.15	$97.20
Purchase #5	$179.97	9.434%	$196.9484	$196.95	$196.95	$196.90
Purchase #6	$80.26	11.140%	$89.201	$89.20	$89.20	$89.20
Purchase #7	$47.51	10.261%	$52.385	$52.39	$52.40	$52.40
7 purchase totals =	$615.16		$671.2611	$671.26	$671.30	$671.30