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	$42.96	10.766%	$47.5851	$47.59	$47.60	$47.60
Purchase #2	$130.32	4.787%	$136.5584	$136.56	$136.55	$136.60
Purchase #3	$221.37	3.384%	$228.8612	$228.86	$228.85	$228.90
Purchase #4	$46.46	13.409%	$52.6898	$52.69	$52.70	$52.70
Purchase #5	$85.44	4.533%	$89.313	$89.31	$89.30	$89.30
Purchase #6	$53.39	13.734%	$60.7226	$60.72	$60.70	$60.70
Purchase #7	$162.80	9.521%	$178.3002	$178.30	$178.30	$178.30
7 purchase totals =	$742.74		$794.0303	$794.03	$794.00	$794.10