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	$244.30	12.712%	$275.3554	$275.36	$275.35	$275.40
Purchase #2	$101.41	13.269%	$114.8661	$114.87	$114.85	$114.90
Purchase #3	$198.27	12.556%	$223.1648	$223.16	$223.15	$223.20
Purchase #4	$197.35	10.578%	$218.2257	$218.23	$218.25	$218.20
Purchase #5	$156.37	9.811%	$171.7115	$171.71	$171.70	$171.70
Purchase #6	$157.99	3.824%	$164.0315	$164.03	$164.05	$164.00
Purchase #7	$30.32	6.313%	$32.2341	$32.23	$32.25	$32.20
7 purchase totals =	$1,086.01		$1,199.5891	$1,199.59	$1,199.60	$1,199.60