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	$250.76	10.164%	$276.2472	$276.25	$276.25	$276.20
Purchase #2	$241.48	10.108%	$265.8888	$265.89	$265.90	$265.90
Purchase #3	$96.62	13.312%	$109.4821	$109.48	$109.50	$109.50
Purchase #4	$135.70	3.470%	$140.4088	$140.41	$140.40	$140.40
Purchase #5	$56.85	5.444%	$59.9449	$59.94	$59.95	$59.90
Purchase #6	$73.43	4.757%	$76.9231	$76.92	$76.90	$76.90
Purchase #7	$94.59	5.528%	$99.8189	$99.82	$99.80	$99.80
7 purchase totals =	$949.43		$1,028.7138	$1,028.71	$1,028.70	$1,028.60