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	$92.56	8.220%	$100.1684	$100.17	$100.15	$100.20
Purchase #2	$173.56	7.596%	$186.7436	$186.74	$186.75	$186.70
Purchase #3	$129.83	7.182%	$139.1544	$139.15	$139.15	$139.20
Purchase #4	$178.36	7.378%	$191.5194	$191.52	$191.50	$191.50
Purchase #5	$225.29	8.662%	$244.8046	$244.80	$244.80	$244.80
Purchase #6	$86.35	4.506%	$90.2409	$90.24	$90.25	$90.20
Purchase #7	$141.36	7.481%	$151.9351	$151.94	$151.95	$151.90
7 purchase totals =	$1,027.31		$1,104.5664	$1,104.56	$1,104.55	$1,104.50