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	$153.92	8.316%	$166.72	$166.72	$166.70	$166.70
Purchase #2	$198.90	7.117%	$213.0557	$213.06	$213.05	$213.10
Purchase #3	$129.82	10.639%	$143.6315	$143.63	$143.65	$143.60
Purchase #4	$105.27	11.395%	$117.2655	$117.27	$117.25	$117.30
Purchase #5	$21.90	3.148%	$22.5894	$22.59	$22.60	$22.60
Purchase #6	$114.73	3.108%	$118.2958	$118.30	$118.30	$118.30
Purchase #7	$232.94	11.330%	$259.3321	$259.33	$259.35	$259.30
7 purchase totals =	$957.48		$1,040.8900	$1,040.90	$1,040.90	$1,040.90