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	$160.52	12.487%	$180.5641	$180.56	$180.55	$180.60
Purchase #2	$55.26	5.824%	$58.4783	$58.48	$58.50	$58.50
Purchase #3	$228.72	5.209%	$240.634	$240.63	$240.65	$240.60
Purchase #4	$247.86	5.264%	$260.9074	$260.91	$260.90	$260.90
Purchase #5	$21.68	13.363%	$24.5771	$24.58	$24.60	$24.60
Purchase #6	$37.89	11.311%	$42.1757	$42.18	$42.20	$42.20
Purchase #7	$82.33	5.139%	$86.5609	$86.56	$86.55	$86.60
7 purchase totals =	$834.26		$893.8975	$893.90	$893.95	$894.00