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	$244.76	13.791%	$278.5149	$278.51	$278.50	$278.50
Purchase #2	$173.25	5.128%	$182.1343	$182.13	$182.15	$182.10
Purchase #3	$34.56	9.479%	$37.8359	$37.84	$37.85	$37.80
Purchase #4	$146.86	12.263%	$164.8694	$164.87	$164.85	$164.90
Purchase #5	$64.34	9.527%	$70.4697	$70.47	$70.45	$70.50
Purchase #6	$202.41	12.553%	$227.8185	$227.82	$227.80	$227.80
Purchase #7	$187.39	11.601%	$209.1291	$209.13	$209.15	$209.10
7 purchase totals =	$1,053.57		$1,170.7718	$1,170.77	$1,170.75	$1,170.70