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	$213.69	11.637%	$238.5571	$238.56	$238.55	$238.60
Purchase #2	$195.97	7.460%	$210.5894	$210.59	$210.60	$210.60
Purchase #3	$122.45	13.561%	$139.0554	$139.06	$139.05	$139.10
Purchase #4	$212.92	6.643%	$227.0643	$227.06	$227.05	$227.10
Purchase #5	$42.54	6.638%	$45.3638	$45.36	$45.35	$45.40
Purchase #6	$168.44	9.586%	$184.5867	$184.59	$184.60	$184.60
Purchase #7	$28.74	10.193%	$31.6695	$31.67	$31.65	$31.70
7 purchase totals =	$984.75		$1,076.8862	$1,076.89	$1,076.85	$1,077.10