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	$121.98	7.661%	$131.3249	$131.32	$131.30	$131.30
Purchase #2	$89.40	10.162%	$98.4848	$98.48	$98.50	$98.50
Purchase #3	$38.75	6.775%	$41.3753	$41.38	$41.40	$41.40
Purchase #4	$184.59	10.585%	$204.1289	$204.13	$204.15	$204.10
Purchase #5	$24.85	3.675%	$25.7632	$25.76	$25.75	$25.80
Purchase #6	$86.73	8.849%	$94.4047	$94.40	$94.40	$94.40
Purchase #7	$87.83	3.460%	$90.8689	$90.87	$90.85	$90.90
7 purchase totals =	$634.13		$686.3507	$686.34	$686.35	$686.40