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	$93.66	10.542%	$103.5336	$103.53	$103.55	$103.50
Purchase #2	$128.44	12.254%	$144.179	$144.18	$144.20	$144.20
Purchase #3	$31.89	11.778%	$35.646	$35.65	$35.65	$35.60
Purchase #4	$90.77	12.521%	$102.1353	$102.14	$102.15	$102.10
Purchase #5	$139.25	7.808%	$150.1226	$150.12	$150.10	$150.10
Purchase #6	$129.51	5.344%	$136.431	$136.43	$136.45	$136.40
Purchase #7	$108.52	8.429%	$117.6672	$117.67	$117.65	$117.70
7 purchase totals =	$722.04		$789.7147	$789.72	$789.75	$789.60