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	$168.90	10.179%	$186.0923	$186.09	$186.10	$186.10
Purchase #2	$84.27	6.227%	$89.5175	$89.52	$89.50	$89.50
Purchase #3	$128.36	10.333%	$141.6234	$141.62	$141.60	$141.60
Purchase #4	$144.55	13.591%	$164.1958	$164.20	$164.20	$164.20
Purchase #5	$210.89	8.682%	$229.1995	$229.20	$229.20	$229.20
Purchase #6	$238.26	12.727%	$268.5834	$268.58	$268.60	$268.60
Purchase #7	$131.99	10.318%	$145.6087	$145.61	$145.60	$145.60
7 purchase totals =	$1,107.22		$1,224.8206	$1,224.82	$1,224.80	$1,224.80