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	$166.34	13.588%	$188.9423	$188.94	$188.95	$188.90
Purchase #2	$128.59	13.195%	$145.5575	$145.56	$145.55	$145.60
Purchase #3	$91.48	13.538%	$103.8646	$103.86	$103.85	$103.90
Purchase #4	$169.46	9.629%	$185.7773	$185.78	$185.80	$185.80
Purchase #5	$149.46	4.118%	$155.6148	$155.61	$155.60	$155.60
Purchase #6	$190.68	4.273%	$198.8278	$198.83	$198.85	$198.80
Purchase #7	$131.52	12.249%	$147.6299	$147.63	$147.65	$147.60
7 purchase totals =	$1,027.53		$1,126.2142	$1,126.21	$1,126.25	$1,126.20