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	$9.34	7.155%	$10.0083	$10.01	$10.00	$10.00
Purchase #2	$38.68	9.675%	$42.4223	$42.42	$42.40	$42.40
Purchase #3	$131.97	6.622%	$140.7091	$140.71	$140.70	$140.70
Purchase #4	$88.25	3.579%	$91.4085	$91.41	$91.40	$91.40
Purchase #5	$206.61	7.715%	$222.55	$222.55	$222.55	$222.60
Purchase #6	$64.61	3.759%	$67.0387	$67.04	$67.05	$67.00
Purchase #7	$241.38	8.838%	$262.7132	$262.71	$262.70	$262.70
7 purchase totals =	$780.84		$836.8501	$836.85	$836.80	$836.80