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	$135.83	5.153%	$142.8293	$142.83	$142.85	$142.80
Purchase #2	$213.43	12.537%	$240.1877	$240.19	$240.20	$240.20
Purchase #3	$167.78	4.578%	$175.461	$175.46	$175.45	$175.50
Purchase #4	$87.63	8.427%	$95.0146	$95.01	$95.00	$95.00
Purchase #5	$155.36	7.256%	$166.6329	$166.63	$166.65	$166.60
Purchase #6	$39.43	8.601%	$42.8214	$42.82	$42.80	$42.80
Purchase #7	$33.99	10.206%	$37.459	$37.46	$37.45	$37.50
7 purchase totals =	$833.45		$900.4059	$900.40	$900.40	$900.40