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	$67.94	8.810%	$73.9255	$73.93	$73.95	$73.90
Purchase #2	$69.64	9.368%	$76.1639	$76.16	$76.15	$76.20
Purchase #3	$134.85	12.746%	$152.038	$152.04	$152.05	$152.00
Purchase #4	$106.53	12.786%	$120.1509	$120.15	$120.15	$120.20
Purchase #5	$16.76	9.386%	$18.3331	$18.33	$18.35	$18.30
Purchase #6	$81.30	9.665%	$89.1576	$89.16	$89.15	$89.20
Purchase #7	$45.86	9.231%	$50.0933	$50.09	$50.10	$50.10
7 purchase totals =	$522.88		$579.8623	$579.86	$579.90	$579.90