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	$128.94	7.691%	$138.8568	$138.86	$138.85	$138.90
Purchase #2	$141.76	13.260%	$160.5574	$160.56	$160.55	$160.60
Purchase #3	$129.59	11.348%	$144.2959	$144.30	$144.30	$144.30
Purchase #4	$231.91	3.624%	$240.3144	$240.31	$240.30	$240.30
Purchase #5	$118.26	8.737%	$128.5924	$128.59	$128.60	$128.60
Purchase #6	$95.55	4.179%	$99.543	$99.54	$99.55	$99.50
Purchase #7	$189.71	13.831%	$215.9488	$215.95	$215.95	$215.90
7 purchase totals =	$1,035.72		$1,128.1087	$1,128.11	$1,128.10	$1,128.10