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	$95.88	4.425%	$100.1227	$100.12	$100.10	$100.10
Purchase #2	$246.27	10.120%	$271.1925	$271.19	$271.20	$271.20
Purchase #3	$27.54	5.449%	$29.0407	$29.04	$29.05	$29.00
Purchase #4	$197.49	13.704%	$224.554	$224.55	$224.55	$224.60
Purchase #5	$79.50	7.313%	$85.3138	$85.31	$85.30	$85.30
Purchase #6	$54.67	13.515%	$62.0587	$62.06	$62.05	$62.10
Purchase #7	$212.34	4.581%	$222.0673	$222.07	$222.05	$222.10
7 purchase totals =	$913.69		$994.3497	$994.34	$994.30	$994.40