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	$80.74	12.573%	$90.8914	$90.89	$90.90	$90.90
Purchase #2	$10.50	4.610%	$10.9841	$10.98	$11.00	$11.00
Purchase #3	$188.59	12.752%	$212.639	$212.64	$212.65	$212.60
Purchase #4	$163.59	3.287%	$168.9672	$168.97	$168.95	$169.00
Purchase #5	$179.74	5.686%	$189.96	$189.96	$189.95	$190.00
Purchase #6	$174.52	8.711%	$189.7224	$189.72	$189.70	$189.70
Purchase #7	$138.80	10.756%	$153.7293	$153.73	$153.75	$153.70
7 purchase totals =	$936.48		$1,016.8934	$1,016.89	$1,016.90	$1,016.90