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	$170.96	4.774%	$179.1216	$179.12	$179.10	$179.10
Purchase #2	$94.57	10.558%	$104.5547	$104.55	$104.55	$104.60
Purchase #3	$144.47	12.191%	$162.0823	$162.08	$162.10	$162.10
Purchase #4	$116.35	9.794%	$127.7453	$127.75	$127.75	$127.70
Purchase #5	$198.76	9.227%	$217.0996	$217.10	$217.10	$217.10
Purchase #6	$59.47	12.404%	$66.8467	$66.85	$66.85	$66.80
Purchase #7	$123.73	4.529%	$129.3337	$129.33	$129.35	$129.30
7 purchase totals =	$908.31		$986.7839	$986.78	$986.80	$986.70