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	$85.92	5.569%	$90.7049	$90.70	$90.70	$90.70
Purchase #2	$237.52	11.285%	$264.3241	$264.32	$264.30	$264.30
Purchase #3	$149.28	7.476%	$160.4402	$160.44	$160.45	$160.40
Purchase #4	$206.66	11.136%	$229.6737	$229.67	$229.65	$229.70
Purchase #5	$237.84	3.576%	$246.3452	$246.35	$246.35	$246.30
Purchase #6	$171.41	10.734%	$189.8091	$189.81	$189.80	$189.80
Purchase #7	$38.71	9.464%	$42.3735	$42.37	$42.35	$42.40
7 purchase totals =	$1,127.34		$1,223.6707	$1,223.66	$1,223.60	$1,223.60