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	$124.66	11.740%	$139.2951	$139.30	$139.30	$139.30
Purchase #2	$116.61	10.341%	$128.6686	$128.67	$128.65	$128.70
Purchase #3	$152.46	6.389%	$162.2007	$162.20	$162.20	$162.20
Purchase #4	$39.93	3.833%	$41.4605	$41.46	$41.45	$41.50
Purchase #5	$169.29	10.180%	$186.5237	$186.52	$186.50	$186.50
Purchase #6	$223.76	4.539%	$233.9165	$233.92	$233.90	$233.90
Purchase #7	$55.89	10.488%	$61.7517	$61.75	$61.75	$61.80
7 purchase totals =	$882.60		$953.8168	$953.82	$953.75	$953.90