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	$130.70	13.154%	$147.8923	$147.89	$147.90	$147.90
Purchase #2	$115.57	6.798%	$123.4264	$123.43	$123.45	$123.40
Purchase #3	$113.90	5.644%	$120.3285	$120.33	$120.35	$120.30
Purchase #4	$153.59	7.389%	$164.9388	$164.94	$164.95	$164.90
Purchase #5	$213.79	8.304%	$231.5431	$231.54	$231.55	$231.50
Purchase #6	$24.49	11.273%	$27.2508	$27.25	$27.25	$27.30
Purchase #7	$237.73	4.667%	$248.8249	$248.82	$248.80	$248.80
7 purchase totals =	$989.77		$1,064.2048	$1,064.20	$1,064.25	$1,064.10