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	$51.53	7.577%	$55.4344	$55.43	$55.45	$55.40
Purchase #2	$154.97	6.398%	$164.885	$164.89	$164.90	$164.90
Purchase #3	$41.83	8.740%	$45.4859	$45.49	$45.50	$45.50
Purchase #4	$156.77	11.770%	$175.2218	$175.22	$175.20	$175.20
Purchase #5	$71.31	5.560%	$75.2748	$75.27	$75.25	$75.30
Purchase #6	$223.87	6.281%	$237.9313	$237.93	$237.95	$237.90
Purchase #7	$61.38	9.871%	$67.4388	$67.44	$67.45	$67.40
7 purchase totals =	$761.66		$821.6720	$821.67	$821.70	$821.60