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	$128.85	7.681%	$138.747	$138.75	$138.75	$138.70
Purchase #2	$165.72	4.231%	$172.7316	$172.73	$172.75	$172.70
Purchase #3	$151.95	5.123%	$159.7344	$159.73	$159.75	$159.70
Purchase #4	$80.88	10.458%	$89.3384	$89.34	$89.35	$89.30
Purchase #5	$136.25	10.753%	$150.901	$150.90	$150.90	$150.90
Purchase #6	$86.43	3.278%	$89.2632	$89.26	$89.25	$89.30
Purchase #7	$123.65	10.699%	$136.8793	$136.88	$136.90	$136.90
7 purchase totals =	$873.73		$937.5949	$937.59	$937.65	$937.50