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	$167.59	6.337%	$178.2102	$178.21	$178.20	$178.20
Purchase #2	$147.73	13.804%	$168.1226	$168.12	$168.10	$168.10
Purchase #3	$42.40	11.620%	$47.3269	$47.33	$47.35	$47.30
Purchase #4	$216.99	3.184%	$223.899	$223.90	$223.90	$223.90
Purchase #5	$161.37	11.218%	$179.4725	$179.47	$179.45	$179.50
Purchase #6	$83.45	6.274%	$88.6857	$88.69	$88.70	$88.70
Purchase #7	$19.80	13.264%	$22.4263	$22.43	$22.45	$22.40
7 purchase totals =	$839.33		$908.1432	$908.15	$908.15	$908.10