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	$188.85	7.753%	$203.4915	$203.49	$203.50	$203.50
Purchase #2	$61.33	10.260%	$67.6225	$67.62	$67.60	$67.60
Purchase #3	$160.50	13.197%	$181.6812	$181.68	$181.70	$181.70
Purchase #4	$60.27	7.650%	$64.8807	$64.88	$64.90	$64.90
Purchase #5	$40.56	4.488%	$42.3803	$42.38	$42.40	$42.40
Purchase #6	$101.77	5.701%	$107.5719	$107.57	$107.55	$107.60
Purchase #7	$99.74	4.832%	$104.5594	$104.56	$104.55	$104.60
7 purchase totals =	$713.02		$772.1875	$772.18	$772.20	$772.30