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	$37.96	11.562%	$42.3489	$42.35	$42.35	$42.30
Purchase #2	$13.94	9.863%	$15.3149	$15.31	$15.30	$15.30
Purchase #3	$74.42	5.334%	$78.3896	$78.39	$78.40	$78.40
Purchase #4	$237.26	5.414%	$250.1053	$250.11	$250.10	$250.10
Purchase #5	$60.32	11.614%	$67.3256	$67.33	$67.35	$67.30
Purchase #6	$111.85	4.593%	$116.9873	$116.99	$117.00	$117.00
Purchase #7	$217.40	12.841%	$245.3163	$245.32	$245.30	$245.30
7 purchase totals =	$753.15		$815.7879	$815.80	$815.80	$815.70