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	$77.54	6.550%	$82.6189	$82.62	$82.60	$82.60
Purchase #2	$132.34	5.527%	$139.6544	$139.65	$139.65	$139.70
Purchase #3	$91.47	9.226%	$99.909	$99.91	$99.90	$99.90
Purchase #4	$22.74	12.413%	$25.5627	$25.56	$25.55	$25.60
Purchase #5	$80.40	9.601%	$88.1192	$88.12	$88.10	$88.10
Purchase #6	$216.30	3.388%	$223.6282	$223.63	$223.65	$223.60
Purchase #7	$144.82	12.284%	$162.6097	$162.61	$162.60	$162.60
7 purchase totals =	$765.61		$822.1021	$822.10	$822.05	$822.10