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	$35.57	12.760%	$40.1087	$40.11	$40.10	$40.10
Purchase #2	$180.76	5.176%	$190.1161	$190.12	$190.10	$190.10
Purchase #3	$153.78	3.226%	$158.7409	$158.74	$158.75	$158.70
Purchase #4	$75.89	10.852%	$84.1256	$84.13	$84.15	$84.10
Purchase #5	$79.91	9.402%	$87.4231	$87.42	$87.40	$87.40
Purchase #6	$174.53	12.436%	$196.2346	$196.23	$196.25	$196.20
Purchase #7	$40.96	7.792%	$44.1516	$44.15	$44.15	$44.20
7 purchase totals =	$741.40		$800.9006	$800.90	$800.90	$800.80