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	$137.76	10.426%	$152.1229	$152.12	$152.10	$152.10
Purchase #2	$73.52	11.581%	$82.0344	$82.03	$82.05	$82.00
Purchase #3	$17.86	12.860%	$20.1568	$20.16	$20.15	$20.20
Purchase #4	$119.33	11.798%	$133.4086	$133.41	$133.40	$133.40
Purchase #5	$143.36	4.200%	$149.3811	$149.38	$149.40	$149.40
Purchase #6	$29.87	12.446%	$33.5876	$33.59	$33.60	$33.60
Purchase #7	$47.59	9.632%	$52.1739	$52.17	$52.15	$52.20
7 purchase totals =	$569.29		$622.8653	$622.86	$622.85	$622.90