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	$76.81	3.598%	$79.5736	$79.57	$79.55	$79.60
Purchase #2	$88.76	13.212%	$100.487	$100.49	$100.50	$100.50
Purchase #3	$150.54	3.216%	$155.3814	$155.38	$155.40	$155.40
Purchase #4	$139.82	10.580%	$154.613	$154.61	$154.60	$154.60
Purchase #5	$39.29	9.236%	$42.9188	$42.92	$42.90	$42.90
Purchase #6	$112.83	6.136%	$119.7532	$119.75	$119.75	$119.80
Purchase #7	$250.37	4.401%	$261.3888	$261.39	$261.40	$261.40
7 purchase totals =	$858.42		$914.1158	$914.11	$914.10	$914.20