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	$165.82	13.664%	$188.4776	$188.48	$188.50	$188.50
Purchase #2	$46.55	12.137%	$52.1998	$52.20	$52.20	$52.20
Purchase #3	$12.59	8.242%	$13.6277	$13.63	$13.65	$13.60
Purchase #4	$31.36	11.634%	$35.0084	$35.01	$35.00	$35.00
Purchase #5	$208.27	13.175%	$235.7096	$235.71	$235.70	$235.70
Purchase #6	$41.27	9.391%	$45.1457	$45.15	$45.15	$45.10
Purchase #7	$85.73	12.586%	$96.52	$96.52	$96.50	$96.50
7 purchase totals =	$591.59		$666.6888	$666.70	$666.70	$666.60