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	$110.97	11.164%	$123.3587	$123.36	$123.35	$123.40
Purchase #2	$52.86	9.304%	$57.7781	$57.78	$57.80	$57.80
Purchase #3	$39.85	6.357%	$42.3833	$42.38	$42.40	$42.40
Purchase #4	$141.25	13.766%	$160.6945	$160.69	$160.70	$160.70
Purchase #5	$41.78	6.781%	$44.6131	$44.61	$44.60	$44.60
Purchase #6	$119.73	10.268%	$132.0239	$132.02	$132.00	$132.00
Purchase #7	$190.89	7.151%	$204.5405	$204.54	$204.55	$204.50
7 purchase totals =	$697.33		$765.3921	$765.38	$765.40	$765.40