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	$59.54	9.836%	$65.3964	$65.40	$65.40	$65.40
Purchase #2	$202.89	9.507%	$222.1788	$222.18	$222.20	$222.20
Purchase #3	$103.83	3.331%	$107.2886	$107.29	$107.30	$107.30
Purchase #4	$63.60	5.707%	$67.2297	$67.23	$67.25	$67.20
Purchase #5	$137.39	3.750%	$142.5421	$142.54	$142.55	$142.50
Purchase #6	$175.41	11.134%	$194.9401	$194.94	$194.95	$194.90
Purchase #7	$44.63	12.675%	$50.2869	$50.29	$50.30	$50.30
7 purchase totals =	$787.29		$849.8626	$849.87	$849.95	$849.80