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	$33.97	6.302%	$36.1108	$36.11	$36.10	$36.10
Purchase #2	$120.37	9.338%	$131.6102	$131.61	$131.60	$131.60
Purchase #3	$150.51	6.692%	$160.5821	$160.58	$160.60	$160.60
Purchase #4	$207.72	7.126%	$222.5221	$222.52	$222.50	$222.50
Purchase #5	$50.67	7.153%	$54.2944	$54.29	$54.30	$54.30
Purchase #6	$75.46	7.629%	$81.2168	$81.22	$81.20	$81.20
Purchase #7	$150.51	13.300%	$170.5278	$170.53	$170.55	$170.50
7 purchase totals =	$789.21		$856.8642	$856.86	$856.85	$856.80