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	$78.83	5.192%	$82.9229	$82.92	$82.90	$82.90
Purchase #2	$62.42	6.349%	$66.383	$66.38	$66.40	$66.40
Purchase #3	$242.77	12.299%	$272.6283	$272.63	$272.65	$272.60
Purchase #4	$142.33	12.296%	$159.8309	$159.83	$159.85	$159.80
Purchase #5	$206.96	7.798%	$223.0987	$223.10	$223.10	$223.10
Purchase #6	$109.56	7.579%	$117.8636	$117.86	$117.85	$117.90
Purchase #7	$11.99	12.775%	$13.5217	$13.52	$13.50	$13.50
7 purchase totals =	$854.86		$936.2491	$936.24	$936.25	$936.20