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	$27.44	8.417%	$29.7496	$29.75	$29.75	$29.70
Purchase #2	$178.31	5.563%	$188.2294	$188.23	$188.25	$188.20
Purchase #3	$6.91	6.409%	$7.3529	$7.35	$7.35	$7.40
Purchase #4	$54.46	9.188%	$59.4638	$59.46	$59.45	$59.50
Purchase #5	$6.90	9.666%	$7.567	$7.57	$7.55	$7.60
Purchase #6	$38.44	13.812%	$43.7493	$43.75	$43.75	$43.70
Purchase #7	$121.96	11.745%	$136.2842	$136.28	$136.30	$136.30
7 purchase totals =	$434.42		$472.3962	$472.39	$472.40	$472.40