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	$223.70	6.495%	$238.2293	$238.23	$238.25	$238.20
Purchase #2	$133.48	13.310%	$151.2462	$151.25	$151.25	$151.20
Purchase #3	$131.53	4.781%	$137.8184	$137.82	$137.80	$137.80
Purchase #4	$62.97	6.791%	$67.2463	$67.25	$67.25	$67.20
Purchase #5	$35.50	11.825%	$39.6979	$39.70	$39.70	$39.70
Purchase #6	$142.97	9.478%	$156.5207	$156.52	$156.50	$156.50
Purchase #7	$79.27	13.139%	$89.6853	$89.69	$89.70	$89.70
7 purchase totals =	$809.42		$880.4441	$880.46	$880.45	$880.30