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	$81.58	11.132%	$90.6615	$90.66	$90.65	$90.70
Purchase #2	$139.40	12.630%	$157.0062	$157.01	$157.00	$157.00
Purchase #3	$61.54	11.361%	$68.5316	$68.53	$68.55	$68.50
Purchase #4	$67.99	4.843%	$71.2828	$71.28	$71.30	$71.30
Purchase #5	$30.56	5.664%	$32.2909	$32.29	$32.30	$32.30
Purchase #6	$26.39	3.526%	$27.3205	$27.32	$27.30	$27.30
Purchase #7	$96.93	6.412%	$103.1452	$103.15	$103.15	$103.10
7 purchase totals =	$504.39		$550.2387	$550.24	$550.25	$550.20