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	$75.77	3.254%	$78.2356	$78.24	$78.25	$78.20
Purchase #2	$224.76	13.425%	$254.934	$254.93	$254.95	$254.90
Purchase #3	$247.30	9.853%	$271.6665	$271.67	$271.65	$271.70
Purchase #4	$151.95	11.571%	$169.5321	$169.53	$169.55	$169.50
Purchase #5	$39.91	5.348%	$42.0444	$42.04	$42.05	$42.00
Purchase #6	$244.62	13.176%	$276.8511	$276.85	$276.85	$276.90
Purchase #7	$142.27	5.692%	$150.368	$150.37	$150.35	$150.40
7 purchase totals =	$1,126.58		$1,243.6317	$1,243.63	$1,243.65	$1,243.60