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	$155.79	7.359%	$167.2546	$167.25	$167.25	$167.30
Purchase #2	$87.64	13.768%	$99.7063	$99.71	$99.70	$99.70
Purchase #3	$116.69	9.837%	$128.1688	$128.17	$128.15	$128.20
Purchase #4	$153.35	7.463%	$164.7945	$164.79	$164.80	$164.80
Purchase #5	$125.30	13.783%	$142.5701	$142.57	$142.55	$142.60
Purchase #6	$142.51	8.389%	$154.4652	$154.47	$154.45	$154.50
Purchase #7	$202.76	9.644%	$222.3142	$222.31	$222.30	$222.30
7 purchase totals =	$984.04		$1,079.2737	$1,079.27	$1,079.20	$1,079.40