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	$137.47	3.406%	$142.1522	$142.15	$142.15	$142.20
Purchase #2	$187.98	4.748%	$196.9053	$196.91	$196.90	$196.90
Purchase #3	$221.45	12.608%	$249.3704	$249.37	$249.35	$249.40
Purchase #4	$203.53	9.440%	$222.7432	$222.74	$222.75	$222.70
Purchase #5	$142.35	11.155%	$158.2291	$158.23	$158.25	$158.20
Purchase #6	$206.58	10.802%	$228.8948	$228.89	$228.90	$228.90
Purchase #7	$44.96	6.682%	$47.9642	$47.96	$47.95	$48.00
7 purchase totals =	$1,144.32		$1,246.2592	$1,246.25	$1,246.25	$1,246.30