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	$138.37	11.243%	$153.9269	$153.93	$153.95	$153.90
Purchase #2	$31.43	13.788%	$35.7636	$35.76	$35.75	$35.80
Purchase #3	$146.44	13.799%	$166.6473	$166.65	$166.65	$166.60
Purchase #4	$200.27	9.783%	$219.8624	$219.86	$219.85	$219.90
Purchase #5	$78.69	7.529%	$84.6146	$84.61	$84.60	$84.60
Purchase #6	$103.62	12.840%	$116.9248	$116.92	$116.90	$116.90
Purchase #7	$83.94	6.127%	$89.083	$89.08	$89.10	$89.10
7 purchase totals =	$782.76		$866.8226	$866.81	$866.80	$866.80