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	$241.53	11.722%	$269.8421	$269.84	$269.85	$269.80
Purchase #2	$11.86	5.732%	$12.5398	$12.54	$12.55	$12.50
Purchase #3	$232.48	3.567%	$240.7726	$240.77	$240.75	$240.80
Purchase #4	$81.63	12.225%	$91.6093	$91.61	$91.60	$91.60
Purchase #5	$83.47	6.816%	$89.1593	$89.16	$89.15	$89.20
Purchase #6	$63.62	10.614%	$70.3726	$70.37	$70.35	$70.40
Purchase #7	$174.68	12.702%	$196.8679	$196.87	$196.85	$196.90
7 purchase totals =	$889.27		$971.1636	$971.16	$971.10	$971.20