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	$93.55	10.817%	$103.6693	$103.67	$103.65	$103.70
Purchase #2	$88.76	6.330%	$94.3785	$94.38	$94.40	$94.40
Purchase #3	$219.39	3.751%	$227.6193	$227.62	$227.60	$227.60
Purchase #4	$54.54	10.602%	$60.3223	$60.32	$60.30	$60.30
Purchase #5	$41.69	9.601%	$45.6927	$45.69	$45.70	$45.70
Purchase #6	$55.70	7.547%	$59.9037	$59.90	$59.90	$59.90
Purchase #7	$178.65	10.859%	$198.0496	$198.05	$198.05	$198.00
7 purchase totals =	$732.28		$789.6354	$789.63	$789.60	$789.60