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	$171.29	5.788%	$181.2043	$181.20	$181.20	$181.20
Purchase #2	$126.55	12.694%	$142.6143	$142.61	$142.60	$142.60
Purchase #3	$79.43	12.625%	$89.458	$89.46	$89.45	$89.50
Purchase #4	$8.48	12.351%	$9.5274	$9.53	$9.55	$9.50
Purchase #5	$86.33	11.780%	$96.4997	$96.50	$96.50	$96.50
Purchase #6	$71.32	12.542%	$80.265	$80.27	$80.25	$80.30
Purchase #7	$49.39	3.174%	$50.9576	$50.96	$50.95	$51.00
7 purchase totals =	$592.79		$650.5263	$650.53	$650.50	$650.60