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	$90.69	9.413%	$99.2266	$99.23	$99.25	$99.20
Purchase #2	$28.84	9.627%	$31.6164	$31.62	$31.60	$31.60
Purchase #3	$166.65	5.298%	$175.4791	$175.48	$175.50	$175.50
Purchase #4	$68.89	13.580%	$78.2453	$78.25	$78.25	$78.20
Purchase #5	$156.80	4.579%	$163.9799	$163.98	$164.00	$164.00
Purchase #6	$120.36	3.789%	$124.9204	$124.92	$124.90	$124.90
Purchase #7	$25.37	10.741%	$28.095	$28.10	$28.10	$28.10
7 purchase totals =	$657.60		$701.5627	$701.58	$701.60	$701.50