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	$73.83	6.534%	$78.6541	$78.65	$78.65	$78.70
Purchase #2	$188.84	11.787%	$211.0986	$211.10	$211.10	$211.10
Purchase #3	$112.72	11.870%	$126.0999	$126.10	$126.10	$126.10
Purchase #4	$61.30	3.338%	$63.3462	$63.35	$63.35	$63.30
Purchase #5	$250.46	8.220%	$271.0478	$271.05	$271.05	$271.00
Purchase #6	$80.72	12.597%	$90.8883	$90.89	$90.90	$90.90
Purchase #7	$80.76	11.457%	$90.0127	$90.01	$90.00	$90.00
7 purchase totals =	$848.63		$931.1476	$931.15	$931.15	$931.10