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	$77.96	3.354%	$80.5748	$80.57	$80.55	$80.60
Purchase #2	$88.27	13.811%	$100.461	$100.46	$100.45	$100.50
Purchase #3	$89.54	9.605%	$98.1403	$98.14	$98.15	$98.10
Purchase #4	$246.39	11.847%	$275.5798	$275.58	$275.60	$275.60
Purchase #5	$196.43	11.296%	$218.6187	$218.62	$218.60	$218.60
Purchase #6	$148.73	5.811%	$157.3727	$157.37	$157.35	$157.40
Purchase #7	$190.92	13.673%	$217.0245	$217.02	$217.00	$217.00
7 purchase totals =	$1,038.24		$1,147.7718	$1,147.76	$1,147.70	$1,147.80