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	$223.62	13.409%	$253.6052	$253.61	$253.60	$253.60
Purchase #2	$162.69	12.691%	$183.337	$183.34	$183.35	$183.30
Purchase #3	$79.43	8.743%	$86.3746	$86.37	$86.35	$86.40
Purchase #4	$157.72	4.429%	$164.7054	$164.71	$164.70	$164.70
Purchase #5	$72.86	10.376%	$80.42	$80.42	$80.40	$80.40
Purchase #6	$52.96	3.488%	$54.8072	$54.81	$54.80	$54.80
Purchase #7	$78.77	12.511%	$88.6249	$88.62	$88.60	$88.60
7 purchase totals =	$828.05		$911.8743	$911.88	$911.80	$911.80