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	$156.42	5.516%	$165.0481	$165.05	$165.05	$165.00
Purchase #2	$79.55	4.225%	$82.911	$82.91	$82.90	$82.90
Purchase #3	$239.40	7.240%	$256.7326	$256.73	$256.75	$256.70
Purchase #4	$45.27	7.134%	$48.4996	$48.50	$48.50	$48.50
Purchase #5	$147.81	5.590%	$156.0726	$156.07	$156.05	$156.10
Purchase #6	$60.71	3.835%	$63.0382	$63.04	$63.05	$63.00
Purchase #7	$56.74	4.191%	$59.118	$59.12	$59.10	$59.10
7 purchase totals =	$785.90		$831.4201	$831.42	$831.40	$831.30