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	$192.78	12.355%	$216.598	$216.60	$216.60	$216.60
Purchase #2	$80.39	11.725%	$89.8157	$89.82	$89.80	$89.80
Purchase #3	$106.85	9.276%	$116.7614	$116.76	$116.75	$116.80
Purchase #4	$216.35	8.606%	$234.9691	$234.97	$234.95	$235.00
Purchase #5	$39.57	8.331%	$42.8666	$42.87	$42.85	$42.90
Purchase #6	$43.35	7.725%	$46.6988	$46.70	$46.70	$46.70
Purchase #7	$54.49	13.471%	$61.8303	$61.83	$61.85	$61.80
7 purchase totals =	$733.78		$809.5399	$809.55	$809.50	$809.60