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	$79.35	12.333%	$89.1362	$89.14	$89.15	$89.10
Purchase #2	$45.66	12.541%	$51.3862	$51.39	$51.40	$51.40
Purchase #3	$242.35	10.352%	$267.4381	$267.44	$267.45	$267.40
Purchase #4	$191.77	10.615%	$212.1264	$212.13	$212.15	$212.10
Purchase #5	$180.42	11.403%	$200.9933	$200.99	$201.00	$201.00
Purchase #6	$23.61	3.516%	$24.4401	$24.44	$24.45	$24.40
Purchase #7	$177.47	13.196%	$200.8889	$200.89	$200.90	$200.90
7 purchase totals =	$940.63		$1,046.4092	$1,046.42	$1,046.50	$1,046.30