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	$85.88	12.491%	$96.6073	$96.61	$96.60	$96.60
Purchase #2	$27.55	3.733%	$28.5784	$28.58	$28.60	$28.60
Purchase #3	$137.66	5.593%	$145.3593	$145.36	$145.35	$145.40
Purchase #4	$52.81	10.386%	$58.2948	$58.29	$58.30	$58.30
Purchase #5	$165.83	5.130%	$174.3371	$174.34	$174.35	$174.30
Purchase #6	$123.96	3.728%	$128.5812	$128.58	$128.60	$128.60
Purchase #7	$99.98	9.171%	$109.1492	$109.15	$109.15	$109.10
7 purchase totals =	$693.67		$740.9073	$740.91	$740.95	$740.90