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	$154.78	8.156%	$167.4039	$167.40	$167.40	$167.40
Purchase #2	$20.43	7.694%	$22.0019	$22.00	$22.00	$22.00
Purchase #3	$52.85	12.261%	$59.3299	$59.33	$59.35	$59.30
Purchase #4	$165.89	11.572%	$185.0868	$185.09	$185.10	$185.10
Purchase #5	$25.56	5.772%	$27.0353	$27.04	$27.05	$27.00
Purchase #6	$246.57	7.758%	$265.6989	$265.70	$265.70	$265.70
Purchase #7	$249.85	9.364%	$273.246	$273.25	$273.25	$273.20
7 purchase totals =	$915.93		$999.8027	$999.81	$999.85	$999.70