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	$166.80	12.730%	$188.0336	$188.03	$188.05	$188.00
Purchase #2	$26.33	11.249%	$29.2919	$29.29	$29.30	$29.30
Purchase #3	$36.80	3.111%	$37.9448	$37.94	$37.95	$37.90
Purchase #4	$63.93	10.180%	$70.4381	$70.44	$70.45	$70.40
Purchase #5	$145.46	11.557%	$162.2708	$162.27	$162.25	$162.30
Purchase #6	$35.48	6.229%	$37.69	$37.69	$37.70	$37.70
Purchase #7	$18.64	10.571%	$20.6104	$20.61	$20.60	$20.60
7 purchase totals =	$493.44		$546.2796	$546.27	$546.30	$546.20