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	$93.67	3.143%	$96.614	$96.61	$96.60	$96.60
Purchase #2	$179.49	3.304%	$185.4203	$185.42	$185.40	$185.40
Purchase #3	$43.75	8.263%	$47.3651	$47.37	$47.35	$47.40
Purchase #4	$215.41	10.124%	$237.2181	$237.22	$237.20	$237.20
Purchase #5	$78.44	5.242%	$82.5518	$82.55	$82.55	$82.60
Purchase #6	$47.33	9.539%	$51.8448	$51.84	$51.85	$51.80
Purchase #7	$11.81	9.535%	$12.9361	$12.94	$12.95	$12.90
7 purchase totals =	$669.90		$713.9502	$713.95	$713.90	$713.90