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	$223.32	8.510%	$242.3245	$242.32	$242.30	$242.30
Purchase #2	$106.96	6.227%	$113.6204	$113.62	$113.60	$113.60
Purchase #3	$168.27	10.112%	$185.2855	$185.29	$185.30	$185.30
Purchase #4	$211.41	8.606%	$229.6039	$229.60	$229.60	$229.60
Purchase #5	$139.64	5.680%	$147.5716	$147.57	$147.55	$147.60
Purchase #6	$96.52	8.175%	$104.4105	$104.41	$104.40	$104.40
Purchase #7	$69.64	11.315%	$77.5198	$77.52	$77.50	$77.50
7 purchase totals =	$1,015.76		$1,100.3362	$1,100.33	$1,100.25	$1,100.30