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	$156.36	5.356%	$164.7346	$164.73	$164.75	$164.70
Purchase #2	$214.65	12.546%	$241.58	$241.58	$241.60	$241.60
Purchase #3	$139.31	7.673%	$149.9993	$150.00	$150.00	$150.00
Purchase #4	$80.55	11.507%	$89.8189	$89.82	$89.80	$89.80
Purchase #5	$137.98	8.591%	$149.8339	$149.83	$149.85	$149.80
Purchase #6	$80.41	12.174%	$90.1991	$90.20	$90.20	$90.20
Purchase #7	$41.65	3.280%	$43.0161	$43.02	$43.00	$43.00
7 purchase totals =	$850.91		$929.1819	$929.18	$929.20	$929.10