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	$109.27	3.420%	$113.007	$113.01	$113.00	$113.00
Purchase #2	$48.99	8.768%	$53.2854	$53.29	$53.30	$53.30
Purchase #3	$28.37	9.800%	$31.1503	$31.15	$31.15	$31.20
Purchase #4	$198.85	8.383%	$215.5196	$215.52	$215.50	$215.50
Purchase #5	$113.25	13.207%	$128.2069	$128.21	$128.20	$128.20
Purchase #6	$22.56	12.229%	$25.3189	$25.32	$25.30	$25.30
Purchase #7	$69.25	3.807%	$71.8863	$71.89	$71.90	$71.90
7 purchase totals =	$590.54		$638.3744	$638.39	$638.35	$638.40