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	$35.77	3.137%	$36.8921	$36.89	$36.90	$36.90
Purchase #2	$143.40	11.803%	$160.3255	$160.33	$160.35	$160.30
Purchase #3	$170.83	12.538%	$192.2487	$192.25	$192.25	$192.20
Purchase #4	$125.55	4.601%	$131.3266	$131.33	$131.35	$131.30
Purchase #5	$229.39	5.733%	$242.5409	$242.54	$242.55	$242.50
Purchase #6	$55.87	9.444%	$61.1464	$61.15	$61.15	$61.10
Purchase #7	$96.33	10.414%	$106.3618	$106.36	$106.35	$106.40
7 purchase totals =	$857.14		$930.8420	$930.85	$930.90	$930.70