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	$31.81	9.532%	$34.8421	$34.84	$34.85	$34.80
Purchase #2	$97.57	13.563%	$110.8034	$110.80	$110.80	$110.80
Purchase #3	$29.67	5.683%	$31.3561	$31.36	$31.35	$31.40
Purchase #4	$123.72	6.256%	$131.4599	$131.46	$131.45	$131.50
Purchase #5	$243.69	10.419%	$269.0801	$269.08	$269.10	$269.10
Purchase #6	$90.49	5.391%	$95.3683	$95.37	$95.35	$95.40
Purchase #7	$142.61	3.716%	$147.9094	$147.91	$147.90	$147.90
7 purchase totals =	$759.56		$820.8193	$820.82	$820.80	$820.90