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	$212.76	12.776%	$239.9422	$239.94	$239.95	$239.90
Purchase #2	$70.27	3.259%	$72.5601	$72.56	$72.55	$72.60
Purchase #3	$50.66	3.802%	$52.5861	$52.59	$52.60	$52.60
Purchase #4	$131.89	3.234%	$136.1553	$136.16	$136.15	$136.20
Purchase #5	$112.34	10.791%	$124.4626	$124.46	$124.45	$124.50
Purchase #6	$79.47	12.301%	$89.2456	$89.25	$89.25	$89.20
Purchase #7	$108.71	5.364%	$114.5412	$114.54	$114.55	$114.50
7 purchase totals =	$766.10		$829.4931	$829.50	$829.50	$829.50