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	$33.50	13.106%	$37.8905	$37.89	$37.90	$37.90
Purchase #2	$114.68	7.835%	$123.6652	$123.67	$123.65	$123.70
Purchase #3	$235.74	7.486%	$253.3875	$253.39	$253.40	$253.40
Purchase #4	$121.32	12.645%	$136.6609	$136.66	$136.65	$136.70
Purchase #5	$86.38	9.399%	$94.4989	$94.50	$94.50	$94.50
Purchase #6	$111.88	6.854%	$119.5483	$119.55	$119.55	$119.50
Purchase #7	$212.26	13.368%	$240.6349	$240.63	$240.65	$240.60
7 purchase totals =	$915.76		$1,006.2862	$1,006.29	$1,006.30	$1,006.30