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	$88.85	12.752%	$100.1802	$100.18	$100.20	$100.20
Purchase #2	$110.51	6.581%	$117.7827	$117.78	$117.80	$117.80
Purchase #3	$131.71	8.261%	$142.5906	$142.59	$142.60	$142.60
Purchase #4	$152.48	13.206%	$172.6165	$172.62	$172.60	$172.60
Purchase #5	$10.30	10.517%	$11.3833	$11.38	$11.40	$11.40
Purchase #6	$114.78	3.849%	$119.1979	$119.20	$119.20	$119.20
Purchase #7	$120.67	4.266%	$125.8178	$125.82	$125.80	$125.80
7 purchase totals =	$729.30		$789.5690	$789.57	$789.60	$789.60