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	$115.40	11.792%	$129.008	$129.01	$129.00	$129.00
Purchase #2	$174.95	12.254%	$196.3884	$196.39	$196.40	$196.40
Purchase #3	$146.42	3.119%	$150.9868	$150.99	$151.00	$151.00
Purchase #4	$146.89	9.486%	$160.824	$160.82	$160.80	$160.80
Purchase #5	$197.75	12.513%	$222.4945	$222.49	$222.50	$222.50
Purchase #6	$133.77	5.692%	$141.3842	$141.38	$141.40	$141.40
Purchase #7	$125.77	4.806%	$131.8145	$131.81	$131.80	$131.80
7 purchase totals =	$1,040.95		$1,132.9004	$1,132.89	$1,132.90	$1,132.90