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	$81.92	9.111%	$89.3837	$89.38	$89.40	$89.40
Purchase #2	$220.84	7.822%	$238.1141	$238.11	$238.10	$238.10
Purchase #3	$154.96	8.577%	$168.2509	$168.25	$168.25	$168.30
Purchase #4	$173.37	6.654%	$184.906	$184.91	$184.90	$184.90
Purchase #5	$111.82	7.874%	$120.6247	$120.62	$120.60	$120.60
Purchase #6	$162.52	5.336%	$171.1921	$171.19	$171.20	$171.20
Purchase #7	$83.99	3.715%	$87.1102	$87.11	$87.10	$87.10
7 purchase totals =	$989.42		$1,059.5817	$1,059.57	$1,059.55	$1,059.60