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	$133.55	7.745%	$143.8934	$143.89	$143.90	$143.90
Purchase #2	$27.78	12.781%	$31.3306	$31.33	$31.35	$31.30
Purchase #3	$240.54	10.423%	$265.6115	$265.61	$265.60	$265.60
Purchase #4	$120.51	12.841%	$135.9847	$135.98	$136.00	$136.00
Purchase #5	$98.68	7.259%	$105.8432	$105.84	$105.85	$105.80
Purchase #6	$46.73	13.508%	$53.0423	$53.04	$53.05	$53.00
Purchase #7	$199.48	8.155%	$215.7476	$215.75	$215.75	$215.70
7 purchase totals =	$867.27		$951.4533	$951.44	$951.50	$951.30