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	$171.44	4.676%	$179.4565	$179.46	$179.45	$179.50
Purchase #2	$243.56	11.703%	$272.0638	$272.06	$272.05	$272.10
Purchase #3	$60.60	10.705%	$67.0872	$67.09	$67.10	$67.10
Purchase #4	$35.44	3.618%	$36.7222	$36.72	$36.70	$36.70
Purchase #5	$143.35	13.371%	$162.5173	$162.52	$162.50	$162.50
Purchase #6	$36.56	8.285%	$39.589	$39.59	$39.60	$39.60
Purchase #7	$195.57	12.203%	$219.4354	$219.44	$219.45	$219.40
7 purchase totals =	$886.52		$976.8714	$976.88	$976.85	$976.90