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	$40.50	7.771%	$43.6473	$43.65	$43.65	$43.60
Purchase #2	$186.48	3.156%	$192.3653	$192.37	$192.35	$192.40
Purchase #3	$145.55	11.670%	$162.5357	$162.54	$162.55	$162.50
Purchase #4	$228.43	9.764%	$250.7339	$250.73	$250.75	$250.70
Purchase #5	$131.81	6.744%	$140.6993	$140.70	$140.70	$140.70
Purchase #6	$6.85	11.237%	$7.6197	$7.62	$7.60	$7.60
Purchase #7	$53.48	10.314%	$58.9959	$59.00	$59.00	$59.00
7 purchase totals =	$793.10		$856.5971	$856.61	$856.60	$856.50