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	$111.50	13.153%	$126.1656	$126.17	$126.15	$126.20
Purchase #2	$107.36	11.700%	$119.9211	$119.92	$119.90	$119.90
Purchase #3	$176.87	5.431%	$186.4758	$186.48	$186.50	$186.50
Purchase #4	$99.32	10.154%	$109.405	$109.41	$109.40	$109.40
Purchase #5	$115.78	7.767%	$124.7726	$124.77	$124.75	$124.80
Purchase #6	$39.95	5.730%	$42.2391	$42.24	$42.25	$42.20
Purchase #7	$101.59	10.142%	$111.8933	$111.89	$111.90	$111.90
7 purchase totals =	$752.37		$820.8725	$820.88	$820.85	$820.90