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	$134.30	6.665%	$143.2511	$143.25	$143.25	$143.30
Purchase #2	$65.73	3.278%	$67.8846	$67.88	$67.90	$67.90
Purchase #3	$213.50	12.585%	$240.369	$240.37	$240.35	$240.40
Purchase #4	$203.92	10.320%	$224.9645	$224.96	$224.95	$225.00
Purchase #5	$220.75	9.221%	$241.1054	$241.11	$241.10	$241.10
Purchase #6	$73.99	12.601%	$83.3135	$83.31	$83.30	$83.30
Purchase #7	$40.86	6.116%	$43.359	$43.36	$43.35	$43.40
7 purchase totals =	$953.05		$1,044.2471	$1,044.24	$1,044.20	$1,044.40