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	$147.47	12.181%	$165.4333	$165.43	$165.45	$165.40
Purchase #2	$71.33	12.521%	$80.2612	$80.26	$80.25	$80.30
Purchase #3	$118.78	5.116%	$124.8568	$124.86	$124.85	$124.90
Purchase #4	$161.29	7.305%	$173.0722	$173.07	$173.05	$173.10
Purchase #5	$42.98	13.866%	$48.9396	$48.94	$48.95	$48.90
Purchase #6	$98.82	12.227%	$110.9027	$110.90	$110.90	$110.90
Purchase #7	$85.72	11.557%	$95.6267	$95.63	$95.65	$95.60
7 purchase totals =	$726.39		$799.0925	$799.09	$799.10	$799.10