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	$118.33	13.744%	$134.5933	$134.59	$134.60	$134.60
Purchase #2	$87.27	4.753%	$91.4179	$91.42	$91.40	$91.40
Purchase #3	$184.58	13.526%	$209.5463	$209.55	$209.55	$209.50
Purchase #4	$123.81	13.757%	$140.8425	$140.84	$140.85	$140.80
Purchase #5	$203.56	11.131%	$226.2183	$226.22	$226.20	$226.20
Purchase #6	$135.92	3.605%	$140.8199	$140.82	$140.80	$140.80
Purchase #7	$127.29	11.791%	$142.2988	$142.30	$142.30	$142.30
7 purchase totals =	$980.76		$1,085.7370	$1,085.74	$1,085.70	$1,085.60