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	$20.42	7.864%	$22.0258	$22.03	$22.05	$22.00
Purchase #2	$51.48	9.521%	$56.3814	$56.38	$56.40	$56.40
Purchase #3	$57.86	3.458%	$59.8608	$59.86	$59.85	$59.90
Purchase #4	$123.41	10.375%	$136.2138	$136.21	$136.20	$136.20
Purchase #5	$198.36	3.704%	$205.7073	$205.71	$205.70	$205.70
Purchase #6	$40.49	9.801%	$44.4584	$44.46	$44.45	$44.50
Purchase #7	$248.31	6.697%	$264.9393	$264.94	$264.95	$264.90
7 purchase totals =	$740.33		$789.5868	$789.59	$789.60	$789.60