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	$117.80	10.343%	$129.9841	$129.98	$130.00	$130.00
Purchase #2	$85.85	3.754%	$89.0728	$89.07	$89.05	$89.10
Purchase #3	$160.92	10.546%	$177.8906	$177.89	$177.90	$177.90
Purchase #4	$220.85	6.238%	$234.6266	$234.63	$234.65	$234.60
Purchase #5	$28.97	7.335%	$31.0949	$31.09	$31.10	$31.10
Purchase #6	$204.63	9.413%	$223.8918	$223.89	$223.90	$223.90
Purchase #7	$171.88	13.679%	$195.3915	$195.39	$195.40	$195.40
7 purchase totals =	$990.90		$1,081.9523	$1,081.94	$1,082.00	$1,082.00