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	$171.54	10.521%	$189.5877	$189.59	$189.60	$189.60
Purchase #2	$154.38	13.808%	$175.6968	$175.70	$175.70	$175.70
Purchase #3	$43.96	6.711%	$46.9102	$46.91	$46.90	$46.90
Purchase #4	$247.50	10.651%	$273.8612	$273.86	$273.85	$273.90
Purchase #5	$140.73	7.129%	$150.7626	$150.76	$150.75	$150.80
Purchase #6	$104.25	9.402%	$114.0516	$114.05	$114.05	$114.10
Purchase #7	$77.93	3.292%	$80.4955	$80.50	$80.50	$80.50
7 purchase totals =	$940.29		$1,031.3656	$1,031.37	$1,031.35	$1,031.50