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	$74.83	8.706%	$81.3447	$81.34	$81.35	$81.30
Purchase #2	$60.29	5.123%	$63.3787	$63.38	$63.40	$63.40
Purchase #3	$37.78	11.172%	$42.0008	$42.00	$42.00	$42.00
Purchase #4	$51.92	6.584%	$55.3384	$55.34	$55.35	$55.30
Purchase #5	$180.89	12.371%	$203.2679	$203.27	$203.25	$203.30
Purchase #6	$33.65	5.322%	$35.4409	$35.44	$35.45	$35.40
Purchase #7	$80.84	13.298%	$91.5901	$91.59	$91.60	$91.60
7 purchase totals =	$520.20		$572.3615	$572.36	$572.40	$572.30