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	$231.52	5.352%	$243.911	$243.91	$243.90	$243.90
Purchase #2	$249.79	9.538%	$273.615	$273.62	$273.60	$273.60
Purchase #3	$100.30	7.109%	$107.4303	$107.43	$107.45	$107.40
Purchase #4	$223.89	8.649%	$243.2542	$243.25	$243.25	$243.30
Purchase #5	$158.53	12.719%	$178.6934	$178.69	$178.70	$178.70
Purchase #6	$40.91	4.663%	$42.8176	$42.82	$42.80	$42.80
Purchase #7	$31.88	3.136%	$32.8798	$32.88	$32.90	$32.90
7 purchase totals =	$1,036.82		$1,122.6013	$1,122.60	$1,122.60	$1,122.60