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	$31.67	4.799%	$33.1898	$33.19	$33.20	$33.20
Purchase #2	$137.45	13.256%	$155.6704	$155.67	$155.65	$155.70
Purchase #3	$124.63	3.345%	$128.7989	$128.80	$128.80	$128.80
Purchase #4	$100.59	8.446%	$109.0858	$109.09	$109.10	$109.10
Purchase #5	$25.41	6.770%	$27.1303	$27.13	$27.15	$27.10
Purchase #6	$63.90	6.190%	$67.8554	$67.86	$67.85	$67.90
Purchase #7	$169.96	12.582%	$191.3444	$191.34	$191.35	$191.30
7 purchase totals =	$653.61		$713.0750	$713.08	$713.10	$713.10