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	$85.78	6.470%	$91.33	$91.33	$91.35	$91.30
Purchase #2	$210.36	10.112%	$231.6316	$231.63	$231.65	$231.60
Purchase #3	$33.81	13.384%	$38.3351	$38.34	$38.35	$38.30
Purchase #4	$21.74	6.139%	$23.0746	$23.07	$23.05	$23.10
Purchase #5	$101.85	3.396%	$105.3088	$105.31	$105.30	$105.30
Purchase #6	$209.31	3.361%	$216.3449	$216.34	$216.35	$216.30
Purchase #7	$29.96	7.188%	$32.1135	$32.11	$32.10	$32.10
7 purchase totals =	$692.81		$738.1385	$738.13	$738.15	$738.00