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	$28.91	7.660%	$31.1245	$31.12	$31.10	$31.10
Purchase #2	$227.47	13.684%	$258.597	$258.60	$258.60	$258.60
Purchase #3	$171.67	6.138%	$182.2071	$182.21	$182.20	$182.20
Purchase #4	$40.58	9.457%	$44.4177	$44.42	$44.40	$44.40
Purchase #5	$131.76	9.705%	$144.5473	$144.55	$144.55	$144.50
Purchase #6	$84.50	4.702%	$88.4732	$88.47	$88.45	$88.50
Purchase #7	$35.83	13.400%	$40.6312	$40.63	$40.65	$40.60
7 purchase totals =	$720.72		$789.9980	$790.00	$789.95	$789.90