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	$211.81	10.709%	$234.4927	$234.49	$234.50	$234.50
Purchase #2	$103.35	5.802%	$109.3464	$109.35	$109.35	$109.30
Purchase #3	$249.52	12.572%	$280.8897	$280.89	$280.90	$280.90
Purchase #4	$236.91	10.760%	$262.4015	$262.40	$262.40	$262.40
Purchase #5	$181.53	12.655%	$204.5026	$204.50	$204.50	$204.50
Purchase #6	$36.37	11.712%	$40.6297	$40.63	$40.65	$40.60
Purchase #7	$178.79	6.467%	$190.3523	$190.35	$190.35	$190.40
7 purchase totals =	$1,198.28		$1,322.6149	$1,322.61	$1,322.65	$1,322.60