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	$94.57	5.814%	$100.0683	$100.07	$100.05	$100.10
Purchase #2	$235.73	13.546%	$267.662	$267.66	$267.65	$267.70
Purchase #3	$68.51	13.563%	$77.802	$77.80	$77.80	$77.80
Purchase #4	$71.72	11.748%	$80.1457	$80.15	$80.15	$80.10
Purchase #5	$79.45	12.323%	$89.2406	$89.24	$89.25	$89.20
Purchase #6	$104.59	4.414%	$109.2066	$109.21	$109.20	$109.20
Purchase #7	$238.92	4.700%	$250.1492	$250.15	$250.15	$250.10
7 purchase totals =	$893.49		$974.2744	$974.28	$974.25	$974.20