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	$81.34	8.759%	$88.4646	$88.46	$88.45	$88.50
Purchase #2	$152.69	5.119%	$160.5062	$160.51	$160.50	$160.50
Purchase #3	$101.92	4.692%	$106.7021	$106.70	$106.70	$106.70
Purchase #4	$145.56	13.743%	$165.5643	$165.56	$165.55	$165.60
Purchase #5	$46.28	13.382%	$52.4732	$52.47	$52.45	$52.50
Purchase #6	$150.74	4.818%	$158.0027	$158.00	$158.00	$158.00
Purchase #7	$173.86	8.328%	$188.3391	$188.34	$188.35	$188.30
7 purchase totals =	$852.39		$920.0522	$920.04	$920.00	$920.10