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	$93.60	6.138%	$99.3452	$99.35	$99.35	$99.30
Purchase #2	$104.65	10.600%	$115.7429	$115.74	$115.75	$115.70
Purchase #3	$80.38	11.703%	$89.7869	$89.79	$89.80	$89.80
Purchase #4	$88.50	4.106%	$92.1338	$92.13	$92.15	$92.10
Purchase #5	$27.68	6.172%	$29.3884	$29.39	$29.40	$29.40
Purchase #6	$7.79	4.807%	$8.1645	$8.16	$8.15	$8.20
Purchase #7	$78.82	4.553%	$82.4087	$82.41	$82.40	$82.40
7 purchase totals =	$481.42		$516.9704	$516.97	$517.00	$516.90