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	$81.71	8.353%	$88.5352	$88.54	$88.55	$88.50
Purchase #2	$123.74	13.267%	$140.1566	$140.16	$140.15	$140.20
Purchase #3	$138.37	3.289%	$142.921	$142.92	$142.90	$142.90
Purchase #4	$246.41	9.227%	$269.1463	$269.15	$269.15	$269.10
Purchase #5	$108.35	9.725%	$118.887	$118.89	$118.90	$118.90
Purchase #6	$59.75	3.368%	$61.7624	$61.76	$61.75	$61.80
Purchase #7	$162.32	3.427%	$167.8827	$167.88	$167.90	$167.90
7 purchase totals =	$920.65		$989.2912	$989.30	$989.30	$989.30