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	$145.25	13.155%	$164.3576	$164.36	$164.35	$164.40
Purchase #2	$106.81	3.791%	$110.8592	$110.86	$110.85	$110.90
Purchase #3	$61.45	10.860%	$68.1235	$68.12	$68.10	$68.10
Purchase #4	$136.47	10.502%	$150.8021	$150.80	$150.80	$150.80
Purchase #5	$171.93	4.257%	$179.2491	$179.25	$179.25	$179.20
Purchase #6	$127.99	7.554%	$137.6584	$137.66	$137.65	$137.70
Purchase #7	$228.39	7.492%	$245.501	$245.50	$245.50	$245.50
7 purchase totals =	$978.29		$1,056.5509	$1,056.55	$1,056.50	$1,056.60