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	$44.45	13.693%	$50.5365	$50.54	$50.55	$50.50
Purchase #2	$97.38	5.302%	$102.5431	$102.54	$102.55	$102.50
Purchase #3	$205.91	3.799%	$213.7325	$213.73	$213.75	$213.70
Purchase #4	$220.39	12.438%	$247.8021	$247.80	$247.80	$247.80
Purchase #5	$156.67	9.156%	$171.0147	$171.01	$171.00	$171.00
Purchase #6	$52.27	13.145%	$59.1409	$59.14	$59.15	$59.10
Purchase #7	$79.99	11.733%	$89.3752	$89.38	$89.40	$89.40
7 purchase totals =	$857.06		$934.1450	$934.14	$934.20	$934.00