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	$52.82	12.276%	$59.3042	$59.30	$59.30	$59.30
Purchase #2	$180.71	8.629%	$196.3035	$196.30	$196.30	$196.30
Purchase #3	$65.71	11.697%	$73.3961	$73.40	$73.40	$73.40
Purchase #4	$224.57	11.693%	$250.829	$250.83	$250.85	$250.80
Purchase #5	$81.94	3.647%	$84.9284	$84.93	$84.95	$84.90
Purchase #6	$174.29	7.225%	$186.8825	$186.88	$186.90	$186.90
Purchase #7	$45.55	6.220%	$48.3832	$48.38	$48.40	$48.40
7 purchase totals =	$825.59		$900.0269	$900.02	$900.10	$900.00