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	$47.53	6.355%	$50.5505	$50.55	$50.55	$50.60
Purchase #2	$184.28	3.787%	$191.2587	$191.26	$191.25	$191.30
Purchase #3	$216.90	12.574%	$244.173	$244.17	$244.15	$244.20
Purchase #4	$129.96	11.586%	$145.0172	$145.02	$145.00	$145.00
Purchase #5	$105.58	10.616%	$116.7884	$116.79	$116.80	$116.80
Purchase #6	$72.57	13.146%	$82.1101	$82.11	$82.10	$82.10
Purchase #7	$91.52	9.340%	$100.068	$100.07	$100.05	$100.10
7 purchase totals =	$848.34		$929.9659	$929.97	$929.90	$930.10