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	$250.30	3.241%	$258.4122	$258.41	$258.40	$258.40
Purchase #2	$94.41	5.443%	$99.5487	$99.55	$99.55	$99.50
Purchase #3	$59.67	13.300%	$67.6061	$67.61	$67.60	$67.60
Purchase #4	$94.57	8.435%	$102.547	$102.55	$102.55	$102.50
Purchase #5	$79.43	11.682%	$88.709	$88.71	$88.70	$88.70
Purchase #6	$198.95	12.681%	$224.1788	$224.18	$224.20	$224.20
Purchase #7	$61.30	9.566%	$67.164	$67.16	$67.15	$67.20
7 purchase totals =	$838.63		$908.1658	$908.17	$908.15	$908.10