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	$170.46	10.421%	$188.2236	$188.22	$188.20	$188.20
Purchase #2	$51.26	10.865%	$56.8294	$56.83	$56.85	$56.80
Purchase #3	$234.50	9.513%	$256.808	$256.81	$256.80	$256.80
Purchase #4	$212.96	3.111%	$219.5852	$219.59	$219.60	$219.60
Purchase #5	$118.34	8.608%	$128.5267	$128.53	$128.55	$128.50
Purchase #6	$145.76	8.452%	$158.0796	$158.08	$158.10	$158.10
Purchase #7	$41.36	3.427%	$42.7774	$42.78	$42.80	$42.80
7 purchase totals =	$974.64		$1,050.8299	$1,050.84	$1,050.90	$1,050.80