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	$99.82	3.536%	$103.3496	$103.35	$103.35	$103.30
Purchase #2	$140.65	13.761%	$160.0048	$160.00	$160.00	$160.00
Purchase #3	$160.92	12.372%	$180.829	$180.83	$180.85	$180.80
Purchase #4	$55.60	4.206%	$57.9385	$57.94	$57.95	$57.90
Purchase #5	$156.69	13.241%	$177.4373	$177.44	$177.45	$177.40
Purchase #6	$231.52	5.506%	$244.2675	$244.27	$244.25	$244.30
Purchase #7	$76.33	11.604%	$85.1873	$85.19	$85.20	$85.20
7 purchase totals =	$921.53		$1,009.0140	$1,009.02	$1,009.05	$1,008.90