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	$69.75	12.220%	$78.2735	$78.27	$78.25	$78.30
Purchase #2	$66.51	8.375%	$72.0802	$72.08	$72.10	$72.10
Purchase #3	$207.63	9.804%	$227.986	$227.99	$228.00	$228.00
Purchase #4	$65.71	10.437%	$72.5682	$72.57	$72.55	$72.60
Purchase #5	$63.77	11.780%	$71.2821	$71.28	$71.30	$71.30
Purchase #6	$68.67	13.757%	$78.1169	$78.12	$78.10	$78.10
Purchase #7	$150.64	13.837%	$171.4841	$171.48	$171.50	$171.50
7 purchase totals =	$692.68		$771.7910	$771.79	$771.80	$771.90