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	$78.61	11.690%	$87.7995	$87.80	$87.80	$87.80
Purchase #2	$40.32	5.567%	$42.5646	$42.56	$42.55	$42.60
Purchase #3	$50.77	11.824%	$56.773	$56.77	$56.75	$56.80
Purchase #4	$105.48	8.626%	$114.5787	$114.58	$114.60	$114.60
Purchase #5	$182.78	7.648%	$196.759	$196.76	$196.75	$196.80
Purchase #6	$239.25	3.218%	$246.9491	$246.95	$246.95	$246.90
Purchase #7	$84.53	4.131%	$88.0219	$88.02	$88.00	$88.00
7 purchase totals =	$781.74		$833.4458	$833.44	$833.40	$833.50