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	$53.73	7.758%	$57.8984	$57.90	$57.90	$57.90
Purchase #2	$150.25	11.795%	$167.972	$167.97	$167.95	$168.00
Purchase #3	$138.95	6.346%	$147.7678	$147.77	$147.75	$147.80
Purchase #4	$241.87	12.102%	$271.1411	$271.14	$271.15	$271.10
Purchase #5	$178.57	6.859%	$190.8181	$190.82	$190.80	$190.80
Purchase #6	$247.47	13.716%	$281.413	$281.41	$281.40	$281.40
Purchase #7	$82.76	9.731%	$90.8134	$90.81	$90.80	$90.80
7 purchase totals =	$1,093.60		$1,207.8238	$1,207.82	$1,207.75	$1,207.80