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	$245.95	11.798%	$274.9672	$274.97	$274.95	$275.00
Purchase #2	$38.81	4.393%	$40.5149	$40.51	$40.50	$40.50
Purchase #3	$135.62	12.335%	$152.3487	$152.35	$152.35	$152.30
Purchase #4	$104.30	8.553%	$113.2208	$113.22	$113.20	$113.20
Purchase #5	$210.94	8.224%	$228.2877	$228.29	$228.30	$228.30
Purchase #6	$77.28	11.718%	$86.3357	$86.34	$86.35	$86.30
Purchase #7	$185.41	10.383%	$204.6611	$204.66	$204.65	$204.70
7 purchase totals =	$998.31		$1,100.3361	$1,100.34	$1,100.30	$1,100.30