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	$90.71	11.117%	$100.7942	$100.79	$100.80	$100.80
Purchase #2	$40.97	12.193%	$45.9655	$45.97	$45.95	$46.00
Purchase #3	$136.68	13.845%	$155.6033	$155.60	$155.60	$155.60
Purchase #4	$114.65	4.347%	$119.6338	$119.63	$119.65	$119.60
Purchase #5	$124.37	13.417%	$141.0567	$141.06	$141.05	$141.10
Purchase #6	$36.61	9.561%	$40.1103	$40.11	$40.10	$40.10
Purchase #7	$207.56	7.145%	$222.3902	$222.39	$222.40	$222.40
7 purchase totals =	$751.55		$825.5540	$825.55	$825.55	$825.60