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	$59.46	13.591%	$67.5412	$67.54	$67.55	$67.50
Purchase #2	$201.93	13.384%	$228.9563	$228.96	$228.95	$229.00
Purchase #3	$19.54	7.230%	$20.9527	$20.95	$20.95	$21.00
Purchase #4	$53.72	10.548%	$59.3864	$59.39	$59.40	$59.40
Purchase #5	$176.82	6.776%	$188.8013	$188.80	$188.80	$188.80
Purchase #6	$186.89	6.784%	$199.5686	$199.57	$199.55	$199.60
Purchase #7	$49.29	8.549%	$53.5038	$53.50	$53.50	$53.50
7 purchase totals =	$747.65		$818.7103	$818.71	$818.70	$818.80