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	$30.83	9.769%	$33.8418	$33.84	$33.85	$33.80
Purchase #2	$240.41	11.200%	$267.3359	$267.34	$267.35	$267.30
Purchase #3	$192.59	3.256%	$198.8607	$198.86	$198.85	$198.90
Purchase #4	$41.73	5.792%	$44.147	$44.15	$44.15	$44.10
Purchase #5	$46.55	11.823%	$52.0536	$52.05	$52.05	$52.10
Purchase #6	$58.82	9.394%	$64.3456	$64.35	$64.35	$64.30
Purchase #7	$71.37	10.574%	$78.9167	$78.92	$78.90	$78.90
7 purchase totals =	$682.30		$739.5013	$739.51	$739.50	$739.40