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	$184.47	3.271%	$190.504	$190.50	$190.50	$190.50
Purchase #2	$55.95	10.641%	$61.9036	$61.90	$61.90	$61.90
Purchase #3	$202.43	13.305%	$229.3633	$229.36	$229.35	$229.40
Purchase #4	$63.80	12.570%	$71.8197	$71.82	$71.80	$71.80
Purchase #5	$77.59	13.298%	$87.9079	$87.91	$87.90	$87.90
Purchase #6	$36.27	9.629%	$39.7624	$39.76	$39.75	$39.80
Purchase #7	$195.57	6.659%	$208.593	$208.59	$208.60	$208.60
7 purchase totals =	$816.08		$889.8539	$889.84	$889.80	$889.90