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	$227.31	5.735%	$240.3462	$240.35	$240.35	$240.30
Purchase #2	$184.52	6.258%	$196.0673	$196.07	$196.05	$196.10
Purchase #3	$148.43	5.561%	$156.6842	$156.68	$156.70	$156.70
Purchase #4	$51.88	11.827%	$58.0158	$58.02	$58.00	$58.00
Purchase #5	$19.25	8.874%	$20.9582	$20.96	$20.95	$21.00
Purchase #6	$28.53	7.288%	$30.6093	$30.61	$30.60	$30.60
Purchase #7	$75.90	8.742%	$82.5352	$82.54	$82.55	$82.50
7 purchase totals =	$735.82		$785.2162	$785.23	$785.20	$785.20