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	$187.83	12.660%	$211.6093	$211.61	$211.60	$211.60
Purchase #2	$182.41	8.775%	$198.4165	$198.42	$198.40	$198.40
Purchase #3	$79.96	13.229%	$90.5379	$90.54	$90.55	$90.50
Purchase #4	$59.76	12.531%	$67.2485	$67.25	$67.25	$67.20
Purchase #5	$148.82	8.866%	$162.0144	$162.01	$162.00	$162.00
Purchase #6	$115.45	7.647%	$124.2785	$124.28	$124.30	$124.30
Purchase #7	$130.25	4.596%	$136.2363	$136.24	$136.25	$136.20
7 purchase totals =	$904.48		$990.3414	$990.35	$990.35	$990.20