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	$239.57	4.497%	$250.3435	$250.34	$250.35	$250.30
Purchase #2	$80.84	11.122%	$89.831	$89.83	$89.85	$89.80
Purchase #3	$238.77	6.441%	$254.1492	$254.15	$254.15	$254.10
Purchase #4	$28.64	8.486%	$31.0704	$31.07	$31.05	$31.10
Purchase #5	$138.84	4.150%	$144.6019	$144.60	$144.60	$144.60
Purchase #6	$220.62	13.195%	$249.7308	$249.73	$249.75	$249.70
Purchase #7	$66.25	6.418%	$70.5019	$70.50	$70.50	$70.50
7 purchase totals =	$1,013.53		$1,090.2287	$1,090.22	$1,090.25	$1,090.10