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	$79.35	13.710%	$90.2289	$90.23	$90.25	$90.20
Purchase #2	$73.91	6.527%	$78.7341	$78.73	$78.75	$78.70
Purchase #3	$170.35	10.273%	$187.8501	$187.85	$187.85	$187.90
Purchase #4	$235.64	9.850%	$258.8505	$258.85	$258.85	$258.90
Purchase #5	$147.81	4.819%	$154.933	$154.93	$154.95	$154.90
Purchase #6	$149.77	9.804%	$164.4535	$164.45	$164.45	$164.50
Purchase #7	$159.72	12.176%	$179.1675	$179.17	$179.15	$179.20
7 purchase totals =	$1,016.55		$1,114.2176	$1,114.21	$1,114.25	$1,114.30