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	$154.58	8.194%	$167.2463	$167.25	$167.25	$167.20
Purchase #2	$65.92	10.230%	$72.6636	$72.66	$72.65	$72.70
Purchase #3	$156.63	9.386%	$171.3313	$171.33	$171.35	$171.30
Purchase #4	$151.42	6.754%	$161.6469	$161.65	$161.65	$161.60
Purchase #5	$18.91	8.355%	$20.4899	$20.49	$20.50	$20.50
Purchase #6	$229.97	9.107%	$250.9134	$250.91	$250.90	$250.90
Purchase #7	$69.90	12.830%	$78.8682	$78.87	$78.85	$78.90
7 purchase totals =	$847.33		$923.1596	$923.16	$923.15	$923.10