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	$140.63	10.697%	$155.6732	$155.67	$155.65	$155.70
Purchase #2	$36.57	4.293%	$38.14	$38.14	$38.15	$38.10
Purchase #3	$90.41	6.661%	$96.4322	$96.43	$96.45	$96.40
Purchase #4	$173.43	6.754%	$185.1435	$185.14	$185.15	$185.10
Purchase #5	$160.89	7.764%	$173.3815	$173.38	$173.40	$173.40
Purchase #6	$93.78	6.369%	$99.7528	$99.75	$99.75	$99.80
Purchase #7	$125.45	12.853%	$141.5741	$141.57	$141.55	$141.60
7 purchase totals =	$821.16		$890.0973	$890.08	$890.10	$890.10