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	$12.59	6.617%	$13.4231	$13.42	$13.40	$13.40
Purchase #2	$118.91	4.535%	$124.3026	$124.30	$124.30	$124.30
Purchase #3	$174.72	3.549%	$180.9208	$180.92	$180.90	$180.90
Purchase #4	$87.31	13.438%	$99.0427	$99.04	$99.05	$99.00
Purchase #5	$196.77	10.238%	$216.9153	$216.92	$216.90	$216.90
Purchase #6	$242.35	5.549%	$255.798	$255.80	$255.80	$255.80
Purchase #7	$5.69	11.800%	$6.3614	$6.36	$6.35	$6.40
7 purchase totals =	$838.34		$896.7639	$896.76	$896.70	$896.70