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	$76.59	5.146%	$80.5313	$80.53	$80.55	$80.50
Purchase #2	$190.59	9.870%	$209.4012	$209.40	$209.40	$209.40
Purchase #3	$118.39	7.358%	$127.1011	$127.10	$127.10	$127.10
Purchase #4	$103.97	5.627%	$109.8204	$109.82	$109.80	$109.80
Purchase #5	$27.64	3.708%	$28.6649	$28.66	$28.65	$28.70
Purchase #6	$240.52	11.484%	$268.1413	$268.14	$268.15	$268.10
Purchase #7	$74.26	8.620%	$80.6612	$80.66	$80.65	$80.70
7 purchase totals =	$831.96		$904.3214	$904.31	$904.30	$904.30