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	$91.72	13.649%	$104.2389	$104.24	$104.25	$104.20
Purchase #2	$243.32	11.579%	$271.494	$271.49	$271.50	$271.50
Purchase #3	$186.52	4.794%	$195.4618	$195.46	$195.45	$195.50
Purchase #4	$23.48	6.218%	$24.94	$24.94	$24.95	$24.90
Purchase #5	$90.99	10.314%	$100.3747	$100.37	$100.35	$100.40
Purchase #6	$89.38	9.517%	$97.8863	$97.89	$97.90	$97.90
Purchase #7	$132.71	7.399%	$142.5292	$142.53	$142.55	$142.50
7 purchase totals =	$858.12		$936.9249	$936.92	$936.95	$936.90