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	$39.86	4.152%	$41.515	$41.52	$41.50	$41.50
Purchase #2	$100.50	10.504%	$111.0565	$111.06	$111.05	$111.10
Purchase #3	$227.50	6.838%	$243.0565	$243.06	$243.05	$243.10
Purchase #4	$96.38	5.738%	$101.9103	$101.91	$101.90	$101.90
Purchase #5	$233.26	10.186%	$257.0199	$257.02	$257.00	$257.00
Purchase #6	$237.40	13.640%	$269.7814	$269.78	$269.80	$269.80
Purchase #7	$185.61	6.874%	$198.3688	$198.37	$198.35	$198.40
7 purchase totals =	$1,120.51		$1,222.7084	$1,222.72	$1,222.65	$1,222.80