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	$242.63	5.496%	$255.9649	$255.96	$255.95	$256.00
Purchase #2	$123.36	11.189%	$137.1628	$137.16	$137.15	$137.20
Purchase #3	$35.86	5.864%	$37.9628	$37.96	$37.95	$38.00
Purchase #4	$32.98	6.428%	$35.1	$35.10	$35.10	$35.10
Purchase #5	$129.82	12.380%	$145.8917	$145.89	$145.90	$145.90
Purchase #6	$146.78	8.732%	$159.5968	$159.60	$159.60	$159.60
Purchase #7	$238.55	12.745%	$268.9532	$268.95	$268.95	$269.00
7 purchase totals =	$949.98		$1,040.6322	$1,040.62	$1,040.60	$1,040.80