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	$121.44	13.490%	$137.8223	$137.82	$137.80	$137.80
Purchase #2	$47.92	9.520%	$52.482	$52.48	$52.50	$52.50
Purchase #3	$33.89	4.854%	$35.535	$35.54	$35.55	$35.50
Purchase #4	$179.39	10.691%	$198.5686	$198.57	$198.55	$198.60
Purchase #5	$202.47	11.300%	$225.3491	$225.35	$225.35	$225.30
Purchase #6	$40.59	13.725%	$46.161	$46.16	$46.15	$46.20
Purchase #7	$38.72	6.806%	$41.3553	$41.36	$41.35	$41.40
7 purchase totals =	$664.42		$737.2733	$737.28	$737.25	$737.30