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	$30.45	9.511%	$33.3461	$33.35	$33.35	$33.30
Purchase #2	$139.73	4.517%	$146.0416	$146.04	$146.05	$146.00
Purchase #3	$9.48	4.447%	$9.9016	$9.90	$9.90	$9.90
Purchase #4	$104.69	3.485%	$108.3384	$108.34	$108.35	$108.30
Purchase #5	$55.66	6.851%	$59.4733	$59.47	$59.45	$59.50
Purchase #6	$93.51	6.248%	$99.3525	$99.35	$99.35	$99.40
Purchase #7	$159.25	3.159%	$164.2807	$164.28	$164.30	$164.30
7 purchase totals =	$592.77		$620.7342	$620.73	$620.75	$620.70