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	$36.30	11.102%	$40.33	$40.33	$40.35	$40.30
Purchase #2	$57.80	11.529%	$64.4638	$64.46	$64.45	$64.50
Purchase #3	$19.69	11.128%	$21.8811	$21.88	$21.90	$21.90
Purchase #4	$71.47	11.280%	$79.5318	$79.53	$79.55	$79.50
Purchase #5	$95.88	7.842%	$103.3989	$103.40	$103.40	$103.40
Purchase #6	$246.82	3.562%	$255.6117	$255.61	$255.60	$255.60
Purchase #7	$90.37	13.862%	$102.8971	$102.90	$102.90	$102.90
7 purchase totals =	$618.33		$668.1144	$668.11	$668.15	$668.10