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	$27.71	6.366%	$29.474	$29.47	$29.45	$29.50
Purchase #2	$97.47	9.155%	$106.3934	$106.39	$106.40	$106.40
Purchase #3	$156.54	12.757%	$176.5098	$176.51	$176.50	$176.50
Purchase #4	$245.47	11.577%	$273.8881	$273.89	$273.90	$273.90
Purchase #5	$98.33	6.641%	$104.8601	$104.86	$104.85	$104.90
Purchase #6	$148.25	6.325%	$157.6268	$157.63	$157.65	$157.60
Purchase #7	$152.73	9.536%	$167.2943	$167.29	$167.30	$167.30
7 purchase totals =	$926.50		$1,016.0465	$1,016.04	$1,016.05	$1,016.10