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	$91.48	9.175%	$99.8733	$99.87	$99.85	$99.90
Purchase #2	$221.47	10.782%	$245.3489	$245.35	$245.35	$245.30
Purchase #3	$181.88	8.192%	$196.7796	$196.78	$196.80	$196.80
Purchase #4	$198.34	6.650%	$211.5296	$211.53	$211.55	$211.50
Purchase #5	$141.44	5.668%	$149.4568	$149.46	$149.45	$149.50
Purchase #6	$248.60	7.749%	$267.864	$267.86	$267.85	$267.90
Purchase #7	$132.93	10.204%	$146.4942	$146.49	$146.50	$146.50
7 purchase totals =	$1,216.14		$1,317.3464	$1,317.34	$1,317.35	$1,317.40