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	$51.74	6.498%	$55.1021	$55.10	$55.10	$55.10
Purchase #2	$95.70	8.679%	$104.0058	$104.01	$104.00	$104.00
Purchase #3	$45.72	11.214%	$50.847	$50.85	$50.85	$50.80
Purchase #4	$130.81	3.108%	$134.8756	$134.88	$134.90	$134.90
Purchase #5	$89.94	4.632%	$94.106	$94.11	$94.10	$94.10
Purchase #6	$223.57	4.484%	$233.5949	$233.59	$233.60	$233.60
Purchase #7	$110.61	4.394%	$115.4702	$115.47	$115.45	$115.50
7 purchase totals =	$748.09		$788.0016	$788.01	$788.00	$788.00