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	$55.46	6.139%	$58.8647	$58.86	$58.85	$58.90
Purchase #2	$89.72	12.282%	$100.7394	$100.74	$100.75	$100.70
Purchase #3	$38.94	8.687%	$42.3227	$42.32	$42.30	$42.30
Purchase #4	$68.62	3.517%	$71.0334	$71.03	$71.05	$71.00
Purchase #5	$57.77	8.336%	$62.5857	$62.59	$62.60	$62.60
Purchase #6	$133.64	4.704%	$139.9264	$139.93	$139.95	$139.90
Purchase #7	$76.73	12.782%	$86.5376	$86.54	$86.55	$86.50
7 purchase totals =	$520.88		$562.0099	$562.01	$562.05	$561.90