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	$15.59	8.563%	$16.925	$16.93	$16.95	$16.90
Purchase #2	$199.61	5.317%	$210.2233	$210.22	$210.20	$210.20
Purchase #3	$80.85	11.814%	$90.4016	$90.40	$90.40	$90.40
Purchase #4	$200.52	11.111%	$222.7998	$222.80	$222.80	$222.80
Purchase #5	$78.89	5.473%	$83.2076	$83.21	$83.20	$83.20
Purchase #6	$137.66	10.189%	$151.6862	$151.69	$151.70	$151.70
Purchase #7	$211.39	3.802%	$219.427	$219.43	$219.45	$219.40
7 purchase totals =	$924.51		$994.6705	$994.68	$994.70	$994.60