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	$19.65	11.414%	$21.8929	$21.89	$21.90	$21.90
Purchase #2	$47.88	6.180%	$50.839	$50.84	$50.85	$50.80
Purchase #3	$203.86	11.297%	$226.8901	$226.89	$226.90	$226.90
Purchase #4	$39.93	7.807%	$43.0473	$43.05	$43.05	$43.00
Purchase #5	$54.76	4.436%	$57.1892	$57.19	$57.20	$57.20
Purchase #6	$189.78	4.541%	$198.3979	$198.40	$198.40	$198.40
Purchase #7	$186.46	4.211%	$194.3118	$194.31	$194.30	$194.30
7 purchase totals =	$742.32		$792.5682	$792.57	$792.60	$792.50