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	$171.81	9.206%	$187.6268	$187.63	$187.65	$187.60
Purchase #2	$161.82	11.754%	$180.8403	$180.84	$180.85	$180.80
Purchase #3	$29.86	10.353%	$32.9514	$32.95	$32.95	$33.00
Purchase #4	$150.86	10.443%	$166.6143	$166.61	$166.60	$166.60
Purchase #5	$26.45	11.577%	$29.5121	$29.51	$29.50	$29.50
Purchase #6	$42.41	3.322%	$43.8189	$43.82	$43.80	$43.80
Purchase #7	$188.34	13.331%	$213.4476	$213.45	$213.45	$213.40
7 purchase totals =	$771.55		$854.8114	$854.81	$854.80	$854.70