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	$123.37	11.169%	$137.1492	$137.15	$137.15	$137.10
Purchase #2	$250.87	8.732%	$272.776	$272.78	$272.80	$272.80
Purchase #3	$121.90	10.676%	$134.914	$134.91	$134.90	$134.90
Purchase #4	$147.73	7.316%	$158.5379	$158.54	$158.55	$158.50
Purchase #5	$104.93	8.133%	$113.464	$113.46	$113.45	$113.50
Purchase #6	$12.69	4.860%	$13.3067	$13.31	$13.30	$13.30
Purchase #7	$165.33	6.440%	$175.9773	$175.98	$176.00	$176.00
7 purchase totals =	$926.82		$1,006.1251	$1,006.13	$1,006.15	$1,006.10