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	$59.53	12.539%	$66.9945	$66.99	$67.00	$67.00
Purchase #2	$249.56	13.690%	$283.7248	$283.72	$283.70	$283.70
Purchase #3	$161.27	9.633%	$176.8051	$176.81	$176.80	$176.80
Purchase #4	$144.61	4.131%	$150.5838	$150.58	$150.60	$150.60
Purchase #5	$130.76	9.282%	$142.8971	$142.90	$142.90	$142.90
Purchase #6	$101.73	12.375%	$114.3191	$114.32	$114.30	$114.30
Purchase #7	$67.44	7.607%	$72.5702	$72.57	$72.55	$72.60
7 purchase totals =	$914.90		$1,007.8946	$1,007.89	$1,007.85	$1,007.90