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	$166.32	11.316%	$185.1408	$185.14	$185.15	$185.10
Purchase #2	$189.34	7.644%	$203.8131	$203.81	$203.80	$203.80
Purchase #3	$111.85	6.673%	$119.3138	$119.31	$119.30	$119.30
Purchase #4	$34.81	7.255%	$37.3355	$37.34	$37.35	$37.30
Purchase #5	$29.89	5.658%	$31.5812	$31.58	$31.60	$31.60
Purchase #6	$96.62	13.586%	$109.7468	$109.75	$109.75	$109.70
Purchase #7	$54.76	13.163%	$61.9681	$61.97	$61.95	$62.00
7 purchase totals =	$683.59		$748.8993	$748.90	$748.90	$748.80