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	$97.30	7.511%	$104.6082	$104.61	$104.60	$104.60
Purchase #2	$239.83	10.529%	$265.0817	$265.08	$265.10	$265.10
Purchase #3	$137.69	7.379%	$147.8501	$147.85	$147.85	$147.90
Purchase #4	$203.95	8.870%	$222.0404	$222.04	$222.05	$222.00
Purchase #5	$37.48	13.355%	$42.4855	$42.49	$42.50	$42.50
Purchase #6	$24.35	4.347%	$25.4085	$25.41	$25.40	$25.40
Purchase #7	$58.95	6.712%	$62.9067	$62.91	$62.90	$62.90
7 purchase totals =	$799.55		$870.3811	$870.39	$870.40	$870.40