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	$250.56	7.457%	$269.2443	$269.24	$269.25	$269.20
Purchase #2	$230.28	6.398%	$245.0133	$245.01	$245.00	$245.00
Purchase #3	$84.44	7.513%	$90.784	$90.78	$90.80	$90.80
Purchase #4	$171.95	3.605%	$178.1488	$178.15	$178.15	$178.10
Purchase #5	$62.59	13.604%	$71.1047	$71.10	$71.10	$71.10
Purchase #6	$162.87	3.722%	$168.932	$168.93	$168.95	$168.90
Purchase #7	$45.80	9.338%	$50.0768	$50.08	$50.10	$50.10
7 purchase totals =	$1,008.49		$1,073.3039	$1,073.29	$1,073.35	$1,073.20