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	$219.41	8.848%	$238.8234	$238.82	$238.80	$238.80
Purchase #2	$130.46	9.531%	$142.8941	$142.89	$142.90	$142.90
Purchase #3	$6.74	13.747%	$7.6665	$7.67	$7.65	$7.70
Purchase #4	$66.91	6.721%	$71.407	$71.41	$71.40	$71.40
Purchase #5	$233.37	11.646%	$260.5483	$260.55	$260.55	$260.50
Purchase #6	$58.34	11.825%	$65.2387	$65.24	$65.25	$65.20
Purchase #7	$154.91	4.172%	$161.3728	$161.37	$161.35	$161.40
7 purchase totals =	$870.14		$947.9508	$947.95	$947.90	$947.90