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	$213.45	8.851%	$232.3425	$232.34	$232.35	$232.30
Purchase #2	$52.39	12.743%	$59.0661	$59.07	$59.05	$59.10
Purchase #3	$154.80	8.860%	$168.5153	$168.52	$168.50	$168.50
Purchase #4	$29.78	6.303%	$31.657	$31.66	$31.65	$31.70
Purchase #5	$75.63	4.398%	$78.9562	$78.96	$78.95	$79.00
Purchase #6	$176.76	8.400%	$191.6078	$191.61	$191.60	$191.60
Purchase #7	$72.96	6.255%	$77.5236	$77.52	$77.50	$77.50
7 purchase totals =	$775.77		$839.6685	$839.68	$839.60	$839.70