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	$36.29	4.302%	$37.8512	$37.85	$37.85	$37.90
Purchase #2	$34.35	12.754%	$38.731	$38.73	$38.75	$38.70
Purchase #3	$48.85	8.575%	$53.0389	$53.04	$53.05	$53.00
Purchase #4	$156.96	9.806%	$172.3515	$172.35	$172.35	$172.40
Purchase #5	$36.68	12.618%	$41.3083	$41.31	$41.30	$41.30
Purchase #6	$71.25	13.376%	$80.7804	$80.78	$80.80	$80.80
Purchase #7	$165.50	8.358%	$179.3325	$179.33	$179.35	$179.30
7 purchase totals =	$549.88		$603.3938	$603.39	$603.45	$603.40