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	$109.86	12.116%	$123.1706	$123.17	$123.15	$123.20
Purchase #2	$78.90	3.423%	$81.6007	$81.60	$81.60	$81.60
Purchase #3	$62.58	6.616%	$66.7203	$66.72	$66.70	$66.70
Purchase #4	$243.76	9.590%	$267.1366	$267.14	$267.15	$267.10
Purchase #5	$212.61	8.652%	$231.005	$231.01	$231.00	$231.00
Purchase #6	$42.51	6.208%	$45.149	$45.15	$45.15	$45.10
Purchase #7	$145.48	11.480%	$162.1811	$162.18	$162.20	$162.20
7 purchase totals =	$895.70		$976.9633	$976.97	$976.95	$976.90