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	$243.62	6.644%	$259.8061	$259.81	$259.80	$259.80
Purchase #2	$138.68	7.332%	$148.848	$148.85	$148.85	$148.80
Purchase #3	$144.53	8.535%	$156.8656	$156.87	$156.85	$156.90
Purchase #4	$249.96	7.610%	$268.982	$268.98	$269.00	$269.00
Purchase #5	$112.63	9.494%	$123.3231	$123.32	$123.30	$123.30
Purchase #6	$55.53	12.632%	$62.5445	$62.54	$62.55	$62.50
Purchase #7	$39.83	3.452%	$41.2049	$41.20	$41.20	$41.20
7 purchase totals =	$984.78		$1,061.5742	$1,061.57	$1,061.55	$1,061.50