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	$206.59	4.696%	$216.2915	$216.29	$216.30	$216.30
Purchase #2	$77.53	3.695%	$80.3947	$80.39	$80.40	$80.40
Purchase #3	$153.66	11.552%	$171.4108	$171.41	$171.40	$171.40
Purchase #4	$43.52	6.504%	$46.3505	$46.35	$46.35	$46.40
Purchase #5	$193.41	8.734%	$210.3024	$210.30	$210.30	$210.30
Purchase #6	$66.50	6.543%	$70.8511	$70.85	$70.85	$70.90
Purchase #7	$124.74	5.648%	$131.7853	$131.79	$131.80	$131.80
7 purchase totals =	$865.95		$927.3863	$927.38	$927.40	$927.50