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	$128.30	12.579%	$144.4389	$144.44	$144.45	$144.40
Purchase #2	$185.89	4.330%	$193.939	$193.94	$193.95	$193.90
Purchase #3	$188.71	12.774%	$212.8158	$212.82	$212.80	$212.80
Purchase #4	$30.44	4.613%	$31.8442	$31.84	$31.85	$31.80
Purchase #5	$26.53	5.421%	$27.9682	$27.97	$27.95	$28.00
Purchase #6	$89.56	13.835%	$101.9506	$101.95	$101.95	$102.00
Purchase #7	$62.96	13.622%	$71.5364	$71.54	$71.55	$71.50
7 purchase totals =	$712.39		$784.4931	$784.50	$784.50	$784.40