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	$29.68	9.286%	$32.4361	$32.44	$32.45	$32.40
Purchase #2	$90.53	8.652%	$98.3627	$98.36	$98.35	$98.40
Purchase #3	$210.41	5.225%	$221.4039	$221.40	$221.40	$221.40
Purchase #4	$202.25	10.799%	$224.091	$224.09	$224.10	$224.10
Purchase #5	$174.56	12.514%	$196.4044	$196.40	$196.40	$196.40
Purchase #6	$133.37	3.703%	$138.3087	$138.31	$138.30	$138.30
Purchase #7	$87.72	5.290%	$92.3604	$92.36	$92.35	$92.40
7 purchase totals =	$928.52		$1,003.3672	$1,003.36	$1,003.35	$1,003.40