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	$223.30	12.351%	$250.8798	$250.88	$250.90	$250.90
Purchase #2	$159.52	6.303%	$169.5745	$169.57	$169.55	$169.60
Purchase #3	$175.94	13.704%	$200.0508	$200.05	$200.05	$200.10
Purchase #4	$135.61	4.341%	$141.4968	$141.50	$141.50	$141.50
Purchase #5	$196.25	8.362%	$212.6604	$212.66	$212.65	$212.70
Purchase #6	$8.90	4.710%	$9.3192	$9.32	$9.30	$9.30
Purchase #7	$41.59	10.334%	$45.8879	$45.89	$45.90	$45.90
7 purchase totals =	$941.11		$1,029.8694	$1,029.87	$1,029.85	$1,030.00