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	$246.47	9.402%	$269.6431	$269.64	$269.65	$269.60
Purchase #2	$182.56	3.196%	$188.3946	$188.39	$188.40	$188.40
Purchase #3	$198.69	5.711%	$210.0372	$210.04	$210.05	$210.00
Purchase #4	$162.43	3.562%	$168.2158	$168.22	$168.20	$168.20
Purchase #5	$52.51	13.229%	$59.4565	$59.46	$59.45	$59.50
Purchase #6	$160.92	5.630%	$169.9798	$169.98	$170.00	$170.00
Purchase #7	$170.87	3.479%	$176.8146	$176.81	$176.80	$176.80
7 purchase totals =	$1,174.45		$1,242.5416	$1,242.54	$1,242.55	$1,242.50