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	$87.32	4.645%	$91.376	$91.38	$91.40	$91.40
Purchase #2	$43.38	8.499%	$47.0669	$47.07	$47.05	$47.10
Purchase #3	$28.39	7.763%	$30.5939	$30.59	$30.60	$30.60
Purchase #4	$152.33	13.246%	$172.5076	$172.51	$172.50	$172.50
Purchase #5	$70.40	13.549%	$79.9385	$79.94	$79.95	$79.90
Purchase #6	$54.98	11.591%	$61.3527	$61.35	$61.35	$61.40
Purchase #7	$64.91	9.441%	$71.0382	$71.04	$71.05	$71.00
7 purchase totals =	$501.71		$553.8738	$553.88	$553.90	$553.90