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	$202.46	5.399%	$213.3908	$213.39	$213.40	$213.40
Purchase #2	$151.98	6.744%	$162.2295	$162.23	$162.25	$162.20
Purchase #3	$72.56	9.606%	$79.5301	$79.53	$79.55	$79.50
Purchase #4	$17.49	5.806%	$18.5055	$18.51	$18.50	$18.50
Purchase #5	$46.40	11.407%	$51.6928	$51.69	$51.70	$51.70
Purchase #6	$179.46	3.672%	$186.0498	$186.05	$186.05	$186.00
Purchase #7	$72.81	7.781%	$78.4753	$78.48	$78.50	$78.50
7 purchase totals =	$743.16		$789.8738	$789.88	$789.95	$789.80