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	$100.96	5.196%	$106.2059	$106.21	$106.20	$106.20
Purchase #2	$83.84	8.323%	$90.818	$90.82	$90.80	$90.80
Purchase #3	$147.66	8.804%	$160.66	$160.66	$160.65	$160.70
Purchase #4	$55.61	9.846%	$61.0854	$61.09	$61.10	$61.10
Purchase #5	$92.34	12.543%	$103.9222	$103.92	$103.90	$103.90
Purchase #6	$85.81	3.616%	$88.9129	$88.91	$88.90	$88.90
Purchase #7	$60.33	10.350%	$66.5742	$66.57	$66.55	$66.60
7 purchase totals =	$626.55		$678.1786	$678.18	$678.10	$678.20