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	$55.46	7.797%	$59.7842	$59.78	$59.80	$59.80
Purchase #2	$224.95	10.363%	$248.2616	$248.26	$248.25	$248.30
Purchase #3	$65.96	6.525%	$70.2639	$70.26	$70.25	$70.30
Purchase #4	$195.96	13.809%	$223.0201	$223.02	$223.00	$223.00
Purchase #5	$217.43	4.597%	$227.4253	$227.43	$227.45	$227.40
Purchase #6	$247.89	10.717%	$274.4564	$274.46	$274.45	$274.50
Purchase #7	$126.89	3.476%	$131.3007	$131.30	$131.30	$131.30
7 purchase totals =	$1,134.54		$1,234.5122	$1,234.51	$1,234.50	$1,234.60