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	$93.81	7.539%	$100.8823	$100.88	$100.90	$100.90
Purchase #2	$235.46	10.336%	$259.7971	$259.80	$259.80	$259.80
Purchase #3	$127.42	11.520%	$142.0988	$142.10	$142.10	$142.10
Purchase #4	$16.36	6.430%	$17.4119	$17.41	$17.40	$17.40
Purchase #5	$88.32	10.169%	$97.3013	$97.30	$97.30	$97.30
Purchase #6	$45.50	10.389%	$50.227	$50.23	$50.25	$50.20
Purchase #7	$69.87	12.847%	$78.8462	$78.85	$78.85	$78.80
7 purchase totals =	$676.74		$746.5646	$746.57	$746.60	$746.50