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	$139.30	3.694%	$144.4457	$144.45	$144.45	$144.40
Purchase #2	$233.99	9.354%	$255.8774	$255.88	$255.90	$255.90
Purchase #3	$154.50	5.175%	$162.4954	$162.50	$162.50	$162.50
Purchase #4	$218.44	4.567%	$228.4162	$228.42	$228.40	$228.40
Purchase #5	$88.81	6.865%	$94.9068	$94.91	$94.90	$94.90
Purchase #6	$144.74	4.275%	$150.9276	$150.93	$150.95	$150.90
Purchase #7	$210.96	5.843%	$223.2864	$223.29	$223.30	$223.30
7 purchase totals =	$1,190.74		$1,260.3555	$1,260.38	$1,260.40	$1,260.30