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	$84.70	6.175%	$89.9302	$89.93	$89.95	$89.90
Purchase #2	$134.34	4.606%	$140.5277	$140.53	$140.55	$140.50
Purchase #3	$19.73	8.267%	$21.3611	$21.36	$21.35	$21.40
Purchase #4	$57.73	11.288%	$64.2466	$64.25	$64.25	$64.20
Purchase #5	$72.70	12.652%	$81.898	$81.90	$81.90	$81.90
Purchase #6	$226.39	10.663%	$250.53	$250.53	$250.55	$250.50
Purchase #7	$62.47	6.331%	$66.425	$66.43	$66.45	$66.40
7 purchase totals =	$658.06		$714.9186	$714.93	$715.00	$714.80