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	$240.44	12.803%	$271.2235	$271.22	$271.20	$271.20
Purchase #2	$107.37	12.590%	$120.8879	$120.89	$120.90	$120.90
Purchase #3	$132.67	5.398%	$139.8315	$139.83	$139.85	$139.80
Purchase #4	$228.77	13.263%	$259.1118	$259.11	$259.10	$259.10
Purchase #5	$19.42	7.790%	$20.9328	$20.93	$20.95	$20.90
Purchase #6	$149.57	12.390%	$168.1017	$168.10	$168.10	$168.10
Purchase #7	$155.70	4.225%	$162.2783	$162.28	$162.30	$162.30
7 purchase totals =	$1,033.94		$1,142.3675	$1,142.36	$1,142.40	$1,142.30