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	$80.49	13.607%	$91.4423	$91.44	$91.45	$91.40
Purchase #2	$201.85	11.141%	$224.3381	$224.34	$224.35	$224.30
Purchase #3	$236.77	10.526%	$261.6924	$261.69	$261.70	$261.70
Purchase #4	$99.38	11.684%	$110.9916	$110.99	$111.00	$111.00
Purchase #5	$143.36	11.326%	$159.597	$159.60	$159.60	$159.60
Purchase #6	$143.28	12.290%	$160.8891	$160.89	$160.90	$160.90
Purchase #7	$80.26	13.706%	$91.2604	$91.26	$91.25	$91.30
7 purchase totals =	$985.39		$1,100.2109	$1,100.21	$1,100.25	$1,100.20