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	$42.90	6.662%	$45.758	$45.76	$45.75	$45.80
Purchase #2	$241.89	7.274%	$259.4851	$259.49	$259.50	$259.50
Purchase #3	$114.67	9.197%	$125.2162	$125.22	$125.20	$125.20
Purchase #4	$248.39	8.139%	$268.6065	$268.61	$268.60	$268.60
Purchase #5	$186.40	5.524%	$196.6967	$196.70	$196.70	$196.70
Purchase #6	$190.93	13.873%	$217.4177	$217.42	$217.40	$217.40
Purchase #7	$196.83	12.232%	$220.9062	$220.91	$220.90	$220.90
7 purchase totals =	$1,222.01		$1,334.0864	$1,334.11	$1,334.05	$1,334.10