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	$221.82	5.553%	$234.1377	$234.14	$234.15	$234.10
Purchase #2	$127.62	3.357%	$131.9042	$131.90	$131.90	$131.90
Purchase #3	$218.44	9.297%	$238.7484	$238.75	$238.75	$238.70
Purchase #4	$222.39	6.290%	$236.3783	$236.38	$236.40	$236.40
Purchase #5	$5.44	5.371%	$5.7322	$5.73	$5.75	$5.70
Purchase #6	$61.36	8.610%	$66.6431	$66.64	$66.65	$66.60
Purchase #7	$86.85	4.226%	$90.5203	$90.52	$90.50	$90.50
7 purchase totals =	$943.92		$1,004.0642	$1,004.06	$1,004.10	$1,003.90