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	$40.30	7.549%	$43.3422	$43.34	$43.35	$43.30
Purchase #2	$186.41	3.851%	$193.5886	$193.59	$193.60	$193.60
Purchase #3	$126.56	11.299%	$140.86	$140.86	$140.85	$140.90
Purchase #4	$45.61	10.764%	$50.5195	$50.52	$50.50	$50.50
Purchase #5	$223.64	7.488%	$240.3862	$240.39	$240.40	$240.40
Purchase #6	$28.61	12.666%	$32.2337	$32.23	$32.25	$32.20
Purchase #7	$32.79	6.322%	$34.863	$34.86	$34.85	$34.90
7 purchase totals =	$683.92		$735.7932	$735.79	$735.80	$735.80