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	$136.27	8.772%	$148.2236	$148.22	$148.20	$148.20
Purchase #2	$69.84	7.118%	$74.8112	$74.81	$74.80	$74.80
Purchase #3	$35.41	11.538%	$39.4956	$39.50	$39.50	$39.50
Purchase #4	$238.41	13.800%	$271.3106	$271.31	$271.30	$271.30
Purchase #5	$131.98	9.366%	$144.3412	$144.34	$144.35	$144.30
Purchase #6	$70.56	11.279%	$78.5185	$78.52	$78.50	$78.50
Purchase #7	$212.41	7.124%	$227.5421	$227.54	$227.55	$227.50
7 purchase totals =	$894.88		$984.2428	$984.24	$984.20	$984.10