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	$174.69	12.720%	$196.9106	$196.91	$196.90	$196.90
Purchase #2	$93.50	4.616%	$97.816	$97.82	$97.80	$97.80
Purchase #3	$228.88	5.264%	$240.9282	$240.93	$240.95	$240.90
Purchase #4	$17.73	8.846%	$19.2984	$19.30	$19.30	$19.30
Purchase #5	$168.87	13.854%	$192.2652	$192.27	$192.25	$192.30
Purchase #6	$115.86	9.863%	$127.2873	$127.29	$127.30	$127.30
Purchase #7	$7.97	4.565%	$8.3338	$8.33	$8.35	$8.30
7 purchase totals =	$807.50		$882.8395	$882.85	$882.85	$882.80