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	$19.50	7.333%	$20.9299	$20.93	$20.95	$20.90
Purchase #2	$241.79	11.429%	$269.4242	$269.42	$269.40	$269.40
Purchase #3	$240.27	3.650%	$249.0399	$249.04	$249.05	$249.00
Purchase #4	$243.86	5.127%	$256.3627	$256.36	$256.35	$256.40
Purchase #5	$141.75	6.446%	$150.8872	$150.89	$150.90	$150.90
Purchase #6	$87.77	3.856%	$91.1544	$91.15	$91.15	$91.20
Purchase #7	$59.30	5.424%	$62.5164	$62.52	$62.50	$62.50
7 purchase totals =	$1,034.24		$1,100.3147	$1,100.31	$1,100.30	$1,100.30