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	$220.27	11.599%	$245.8191	$245.82	$245.80	$245.80
Purchase #2	$111.84	7.352%	$120.0625	$120.06	$120.05	$120.10
Purchase #3	$35.82	4.683%	$37.4975	$37.50	$37.50	$37.50
Purchase #4	$37.87	13.735%	$43.0714	$43.07	$43.05	$43.10
Purchase #5	$85.35	7.474%	$91.7291	$91.73	$91.75	$91.70
Purchase #6	$75.98	8.561%	$82.4846	$82.48	$82.50	$82.50
Purchase #7	$13.72	13.678%	$15.5966	$15.60	$15.60	$15.60
7 purchase totals =	$580.85		$636.2608	$636.26	$636.25	$636.30