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	$230.50	10.641%	$255.0275	$255.03	$255.05	$255.00
Purchase #2	$53.31	6.862%	$56.9681	$56.97	$56.95	$57.00
Purchase #3	$20.53	4.110%	$21.3738	$21.37	$21.35	$21.40
Purchase #4	$78.69	10.614%	$87.0422	$87.04	$87.05	$87.00
Purchase #5	$64.27	11.375%	$71.5807	$71.58	$71.60	$71.60
Purchase #6	$98.37	11.731%	$109.9098	$109.91	$109.90	$109.90
Purchase #7	$75.48	7.334%	$81.0157	$81.02	$81.00	$81.00
7 purchase totals =	$621.15		$682.9178	$682.92	$682.90	$682.90