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	$54.43	3.828%	$56.5136	$56.51	$56.50	$56.50
Purchase #2	$69.99	12.501%	$78.7394	$78.74	$78.75	$78.70
Purchase #3	$51.40	4.839%	$53.8872	$53.89	$53.90	$53.90
Purchase #4	$139.89	6.630%	$149.1647	$149.16	$149.15	$149.20
Purchase #5	$56.52	5.691%	$59.7366	$59.74	$59.75	$59.70
Purchase #6	$203.86	4.762%	$213.5678	$213.57	$213.55	$213.60
Purchase #7	$194.33	12.645%	$218.903	$218.90	$218.90	$218.90
7 purchase totals =	$770.42		$830.5123	$830.51	$830.50	$830.50