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	$106.59	10.265%	$117.5315	$117.53	$117.55	$117.50
Purchase #2	$33.98	5.626%	$35.8917	$35.89	$35.90	$35.90
Purchase #3	$197.29	11.780%	$220.5308	$220.53	$220.55	$220.50
Purchase #4	$191.73	13.777%	$218.1446	$218.14	$218.15	$218.10
Purchase #5	$43.57	4.468%	$45.5167	$45.52	$45.50	$45.50
Purchase #6	$5.96	8.180%	$6.4475	$6.45	$6.45	$6.40
Purchase #7	$167.42	8.423%	$181.5218	$181.52	$181.50	$181.50
7 purchase totals =	$746.54		$825.5846	$825.58	$825.60	$825.40