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	$111.56	7.640%	$120.0832	$120.08	$120.10	$120.10
Purchase #2	$92.95	4.702%	$97.3205	$97.32	$97.30	$97.30
Purchase #3	$89.36	7.608%	$96.1585	$96.16	$96.15	$96.20
Purchase #4	$169.58	11.187%	$188.5509	$188.55	$188.55	$188.60
Purchase #5	$37.91	11.731%	$42.3572	$42.36	$42.35	$42.40
Purchase #6	$64.32	11.160%	$71.4981	$71.50	$71.50	$71.50
Purchase #7	$55.80	6.721%	$59.5503	$59.55	$59.55	$59.60
7 purchase totals =	$621.48		$675.5187	$675.52	$675.50	$675.70