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	$137.26	3.648%	$142.2672	$142.27	$142.25	$142.30
Purchase #2	$27.79	6.196%	$29.5119	$29.51	$29.50	$29.50
Purchase #3	$24.89	9.485%	$27.2508	$27.25	$27.25	$27.30
Purchase #4	$177.49	6.424%	$188.892	$188.89	$188.90	$188.90
Purchase #5	$64.72	9.611%	$70.9402	$70.94	$70.95	$70.90
Purchase #6	$28.56	8.228%	$30.9099	$30.91	$30.90	$30.90
Purchase #7	$18.57	9.453%	$20.3254	$20.33	$20.35	$20.30
7 purchase totals =	$479.28		$510.0974	$510.10	$510.10	$510.10