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	$48.27	12.438%	$54.2738	$54.27	$54.25	$54.30
Purchase #2	$160.52	6.664%	$171.2171	$171.22	$171.20	$171.20
Purchase #3	$6.89	12.785%	$7.7709	$7.77	$7.75	$7.80
Purchase #4	$158.30	10.263%	$174.5463	$174.55	$174.55	$174.50
Purchase #5	$96.80	4.504%	$101.1599	$101.16	$101.15	$101.20
Purchase #6	$168.50	5.824%	$178.3134	$178.31	$178.30	$178.30
Purchase #7	$31.61	7.475%	$33.9728	$33.97	$33.95	$34.00
7 purchase totals =	$670.89		$721.2542	$721.25	$721.15	$721.30