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	$144.34	4.186%	$150.3821	$150.38	$150.40	$150.40
Purchase #2	$243.89	13.351%	$276.4518	$276.45	$276.45	$276.50
Purchase #3	$194.81	5.587%	$205.694	$205.69	$205.70	$205.70
Purchase #4	$84.84	9.152%	$92.6046	$92.60	$92.60	$92.60
Purchase #5	$168.86	12.872%	$190.5957	$190.60	$190.60	$190.60
Purchase #6	$212.72	7.550%	$228.7804	$228.78	$228.80	$228.80
Purchase #7	$136.81	13.529%	$155.319	$155.32	$155.30	$155.30
7 purchase totals =	$1,186.27		$1,299.8276	$1,299.82	$1,299.85	$1,299.90