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	$10.71	11.649%	$11.9576	$11.96	$11.95	$12.00
Purchase #2	$82.98	7.707%	$89.3753	$89.38	$89.40	$89.40
Purchase #3	$186.81	5.388%	$196.8753	$196.88	$196.90	$196.90
Purchase #4	$63.55	6.687%	$67.7996	$67.80	$67.80	$67.80
Purchase #5	$201.49	7.668%	$216.9403	$216.94	$216.95	$216.90
Purchase #6	$156.80	7.353%	$168.3295	$168.33	$168.35	$168.30
Purchase #7	$74.33	9.112%	$81.1029	$81.10	$81.10	$81.10
7 purchase totals =	$776.67		$832.3805	$832.39	$832.45	$832.40