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	$114.88	4.285%	$119.8026	$119.80	$119.80	$119.80
Purchase #2	$114.61	7.465%	$123.1656	$123.17	$123.15	$123.20
Purchase #3	$67.93	6.821%	$72.5635	$72.56	$72.55	$72.60
Purchase #4	$243.68	13.642%	$276.9228	$276.92	$276.90	$276.90
Purchase #5	$150.31	7.827%	$162.0748	$162.07	$162.05	$162.10
Purchase #6	$40.55	3.652%	$42.0309	$42.03	$42.05	$42.00
Purchase #7	$108.55	7.483%	$116.6728	$116.67	$116.65	$116.70
7 purchase totals =	$840.51		$913.2330	$913.22	$913.15	$913.30