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	$46.90	12.139%	$52.5932	$52.59	$52.60	$52.60
Purchase #2	$174.48	6.342%	$185.5455	$185.55	$185.55	$185.50
Purchase #3	$88.59	10.451%	$97.8485	$97.85	$97.85	$97.80
Purchase #4	$195.74	12.787%	$220.7693	$220.77	$220.75	$220.80
Purchase #5	$19.94	9.166%	$21.7677	$21.77	$21.75	$21.80
Purchase #6	$24.62	6.328%	$26.178	$26.18	$26.20	$26.20
Purchase #7	$55.48	12.465%	$62.3956	$62.40	$62.40	$62.40
7 purchase totals =	$605.75		$667.0978	$667.11	$667.10	$667.10