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	$104.56	12.744%	$117.8851	$117.89	$117.90	$117.90
Purchase #2	$142.75	11.700%	$159.4518	$159.45	$159.45	$159.50
Purchase #3	$38.45	11.874%	$43.0156	$43.02	$43.00	$43.00
Purchase #4	$184.96	7.293%	$198.4491	$198.45	$198.45	$198.40
Purchase #5	$27.47	4.453%	$28.6932	$28.69	$28.70	$28.70
Purchase #6	$96.87	4.212%	$100.9502	$100.95	$100.95	$101.00
Purchase #7	$120.86	6.630%	$128.873	$128.87	$128.85	$128.90
7 purchase totals =	$715.92		$777.3180	$777.32	$777.30	$777.40