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	$6.34	11.790%	$7.0875	$7.09	$7.10	$7.10
Purchase #2	$19.54	4.807%	$20.4793	$20.48	$20.50	$20.50
Purchase #3	$152.55	8.577%	$165.6342	$165.63	$165.65	$165.60
Purchase #4	$148.42	4.800%	$155.5442	$155.54	$155.55	$155.50
Purchase #5	$50.34	10.129%	$55.4389	$55.44	$55.45	$55.40
Purchase #6	$198.67	11.638%	$221.7912	$221.79	$221.80	$221.80
Purchase #7	$17.60	10.633%	$19.4714	$19.47	$19.45	$19.50
7 purchase totals =	$593.46		$645.4467	$645.44	$645.50	$645.40