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	$114.51	11.713%	$127.9226	$127.92	$127.90	$127.90
Purchase #2	$237.58	9.437%	$260.0004	$260.00	$260.00	$260.00
Purchase #3	$83.44	10.526%	$92.2229	$92.22	$92.20	$92.20
Purchase #4	$204.86	12.826%	$231.1353	$231.14	$231.15	$231.10
Purchase #5	$127.50	5.770%	$134.8568	$134.86	$134.85	$134.90
Purchase #6	$198.33	12.635%	$223.389	$223.39	$223.40	$223.40
Purchase #7	$218.33	10.151%	$240.4927	$240.49	$240.50	$240.50
7 purchase totals =	$1,184.55		$1,310.0197	$1,310.02	$1,310.00	$1,310.00