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	$169.46	4.548%	$177.167	$177.17	$177.15	$177.20
Purchase #2	$135.94	3.833%	$141.1506	$141.15	$141.15	$141.20
Purchase #3	$133.89	8.611%	$145.4193	$145.42	$145.40	$145.40
Purchase #4	$139.63	9.154%	$152.4117	$152.41	$152.40	$152.40
Purchase #5	$143.90	4.817%	$150.8317	$150.83	$150.85	$150.80
Purchase #6	$92.25	9.808%	$101.2979	$101.30	$101.30	$101.30
Purchase #7	$122.55	7.344%	$131.5501	$131.55	$131.55	$131.60
7 purchase totals =	$937.62		$999.8283	$999.83	$999.80	$999.90