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	$34.28	6.749%	$36.5936	$36.59	$36.60	$36.60
Purchase #2	$126.83	10.363%	$139.9734	$139.97	$139.95	$140.00
Purchase #3	$80.76	6.656%	$86.1354	$86.14	$86.15	$86.10
Purchase #4	$149.47	11.809%	$167.1209	$167.12	$167.10	$167.10
Purchase #5	$243.72	7.719%	$262.5327	$262.53	$262.55	$262.50
Purchase #6	$250.47	5.367%	$263.9127	$263.91	$263.90	$263.90
Purchase #7	$80.53	7.823%	$86.8299	$86.83	$86.85	$86.80
7 purchase totals =	$966.06		$1,043.0986	$1,043.09	$1,043.10	$1,043.00