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	$69.48	13.583%	$78.9175	$78.92	$78.90	$78.90
Purchase #2	$67.50	6.739%	$72.0488	$72.05	$72.05	$72.00
Purchase #3	$71.45	9.672%	$78.3606	$78.36	$78.35	$78.40
Purchase #4	$38.98	8.862%	$42.4344	$42.43	$42.45	$42.40
Purchase #5	$98.63	7.177%	$105.7087	$105.71	$105.70	$105.70
Purchase #6	$234.46	11.744%	$261.995	$262.00	$262.00	$262.00
Purchase #7	$114.64	8.309%	$124.1654	$124.17	$124.15	$124.20
7 purchase totals =	$695.14		$763.6304	$763.64	$763.60	$763.60