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	$139.79	11.213%	$155.4647	$155.46	$155.45	$155.50
Purchase #2	$80.62	10.739%	$89.2778	$89.28	$89.30	$89.30
Purchase #3	$166.57	12.151%	$186.8099	$186.81	$186.80	$186.80
Purchase #4	$180.30	4.793%	$188.9418	$188.94	$188.95	$188.90
Purchase #5	$125.31	3.515%	$129.7146	$129.71	$129.70	$129.70
Purchase #6	$138.42	7.484%	$148.7794	$148.78	$148.80	$148.80
Purchase #7	$172.43	11.111%	$191.5887	$191.59	$191.60	$191.60
7 purchase totals =	$1,003.44		$1,090.5769	$1,090.57	$1,090.60	$1,090.60