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	$165.34	5.794%	$174.9198	$174.92	$174.90	$174.90
Purchase #2	$187.37	7.161%	$200.7876	$200.79	$200.80	$200.80
Purchase #3	$144.37	4.751%	$151.229	$151.23	$151.25	$151.20
Purchase #4	$239.32	11.730%	$267.3922	$267.39	$267.40	$267.40
Purchase #5	$71.78	9.248%	$78.4182	$78.42	$78.40	$78.40
Purchase #6	$197.73	7.296%	$212.1564	$212.16	$212.15	$212.20
Purchase #7	$208.79	11.824%	$233.4773	$233.48	$233.50	$233.50
7 purchase totals =	$1,214.70		$1,318.3805	$1,318.39	$1,318.40	$1,318.40