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	$180.44	6.313%	$191.8312	$191.83	$191.85	$191.80
Purchase #2	$99.77	9.363%	$109.1115	$109.11	$109.10	$109.10
Purchase #3	$59.41	11.673%	$66.3449	$66.34	$66.35	$66.30
Purchase #4	$204.47	8.393%	$221.6312	$221.63	$221.65	$221.60
Purchase #5	$156.76	6.861%	$167.5153	$167.52	$167.50	$167.50
Purchase #6	$72.97	11.218%	$81.1558	$81.16	$81.15	$81.20
Purchase #7	$26.34	9.182%	$28.7585	$28.76	$28.75	$28.80
7 purchase totals =	$800.16		$866.3484	$866.35	$866.35	$866.30