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	$135.36	3.482%	$140.0732	$140.07	$140.05	$140.10
Purchase #2	$152.39	3.392%	$157.5591	$157.56	$157.55	$157.60
Purchase #3	$187.68	11.341%	$208.9648	$208.96	$208.95	$209.00
Purchase #4	$118.44	13.404%	$134.3157	$134.32	$134.30	$134.30
Purchase #5	$41.72	5.536%	$44.0296	$44.03	$44.05	$44.00
Purchase #6	$82.48	8.626%	$89.5947	$89.59	$89.60	$89.60
Purchase #7	$90.41	10.549%	$99.9474	$99.95	$99.95	$99.90
7 purchase totals =	$808.48		$874.4845	$874.48	$874.45	$874.50