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	$71.85	12.120%	$80.5582	$80.56	$80.55	$80.60
Purchase #2	$117.37	9.849%	$128.9298	$128.93	$128.95	$128.90
Purchase #3	$234.39	8.156%	$253.5068	$253.51	$253.50	$253.50
Purchase #4	$31.53	12.264%	$35.3968	$35.40	$35.40	$35.40
Purchase #5	$50.46	12.486%	$56.7604	$56.76	$56.75	$56.80
Purchase #6	$53.83	5.641%	$56.8666	$56.87	$56.85	$56.90
Purchase #7	$91.73	6.196%	$97.4136	$97.41	$97.40	$97.40
7 purchase totals =	$651.16		$709.4322	$709.44	$709.40	$709.50