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	$170.92	7.872%	$184.3748	$184.37	$184.35	$184.40
Purchase #2	$156.66	6.310%	$166.5452	$166.55	$166.55	$166.50
Purchase #3	$9.78	4.609%	$10.2308	$10.23	$10.25	$10.20
Purchase #4	$224.72	11.290%	$250.0909	$250.09	$250.10	$250.10
Purchase #5	$49.38	7.726%	$53.1951	$53.20	$53.20	$53.20
Purchase #6	$83.48	8.457%	$90.5399	$90.54	$90.55	$90.50
Purchase #7	$17.85	5.275%	$18.7916	$18.79	$18.80	$18.80
7 purchase totals =	$712.79		$773.7683	$773.77	$773.80	$773.70