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	$45.68	11.391%	$50.8834	$50.88	$50.90	$50.90
Purchase #2	$31.42	6.123%	$33.3438	$33.34	$33.35	$33.30
Purchase #3	$25.43	7.723%	$27.394	$27.39	$27.40	$27.40
Purchase #4	$186.78	12.744%	$210.5832	$210.58	$210.60	$210.60
Purchase #5	$77.69	12.253%	$87.2094	$87.21	$87.20	$87.20
Purchase #6	$242.38	5.490%	$255.6867	$255.69	$255.70	$255.70
Purchase #7	$155.25	5.851%	$164.3337	$164.33	$164.35	$164.30
7 purchase totals =	$764.63		$829.4342	$829.42	$829.50	$829.40