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	$81.99	4.228%	$85.4565	$85.46	$85.45	$85.50
Purchase #2	$213.31	4.860%	$223.6769	$223.68	$223.70	$223.70
Purchase #3	$80.70	8.857%	$87.8476	$87.85	$87.85	$87.80
Purchase #4	$33.55	11.195%	$37.3059	$37.31	$37.30	$37.30
Purchase #5	$199.70	4.494%	$208.6745	$208.67	$208.65	$208.70
Purchase #6	$87.76	9.160%	$95.7988	$95.80	$95.80	$95.80
Purchase #7	$95.36	4.299%	$99.4595	$99.46	$99.45	$99.50
7 purchase totals =	$792.37		$838.2197	$838.23	$838.20	$838.30