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	$219.43	13.687%	$249.4634	$249.46	$249.45	$249.50
Purchase #2	$157.98	9.648%	$173.2219	$173.22	$173.20	$173.20
Purchase #3	$199.69	11.179%	$222.0133	$222.01	$222.00	$222.00
Purchase #4	$96.76	3.714%	$100.3537	$100.35	$100.35	$100.40
Purchase #5	$123.48	6.819%	$131.9001	$131.90	$131.90	$131.90
Purchase #6	$18.79	12.637%	$21.1645	$21.16	$21.15	$21.20
Purchase #7	$172.62	3.173%	$178.0972	$178.10	$178.10	$178.10
7 purchase totals =	$988.75		$1,076.2141	$1,076.20	$1,076.15	$1,076.30