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	$98.28	6.588%	$104.7547	$104.75	$104.75	$104.80
Purchase #2	$66.41	7.588%	$71.4492	$71.45	$71.45	$71.40
Purchase #3	$169.63	6.835%	$181.2242	$181.22	$181.20	$181.20
Purchase #4	$190.55	6.702%	$203.3207	$203.32	$203.30	$203.30
Purchase #5	$129.95	7.106%	$139.1842	$139.18	$139.20	$139.20
Purchase #6	$90.96	10.568%	$100.5727	$100.57	$100.55	$100.60
Purchase #7	$187.62	4.513%	$196.0873	$196.09	$196.10	$196.10
7 purchase totals =	$933.40		$996.5930	$996.58	$996.55	$996.60