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	$127.36	10.310%	$140.4908	$140.49	$140.50	$140.50
Purchase #2	$130.53	9.626%	$143.0948	$143.09	$143.10	$143.10
Purchase #3	$55.47	6.324%	$58.9779	$58.98	$59.00	$59.00
Purchase #4	$182.37	9.594%	$199.8666	$199.87	$199.85	$199.90
Purchase #5	$38.64	8.163%	$41.7942	$41.79	$41.80	$41.80
Purchase #6	$174.28	3.219%	$179.8901	$179.89	$179.90	$179.90
Purchase #7	$43.61	3.428%	$45.105	$45.11	$45.10	$45.10
7 purchase totals =	$752.26		$809.2194	$809.22	$809.25	$809.30