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	$117.69	10.108%	$129.5861	$129.59	$129.60	$129.60
Purchase #2	$92.41	7.396%	$99.2446	$99.24	$99.25	$99.20
Purchase #3	$84.28	4.584%	$88.1434	$88.14	$88.15	$88.10
Purchase #4	$84.98	3.746%	$88.1634	$88.16	$88.15	$88.20
Purchase #5	$182.77	7.436%	$196.3608	$196.36	$196.35	$196.40
Purchase #6	$72.89	13.105%	$82.4422	$82.44	$82.45	$82.40
Purchase #7	$199.78	3.504%	$206.7803	$206.78	$206.80	$206.80
7 purchase totals =	$834.80		$890.7208	$890.71	$890.75	$890.70