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	$109.41	6.323%	$116.328	$116.33	$116.35	$116.30
Purchase #2	$237.94	5.234%	$250.3938	$250.39	$250.40	$250.40
Purchase #3	$188.77	6.223%	$200.5172	$200.52	$200.50	$200.50
Purchase #4	$156.33	5.171%	$164.4138	$164.41	$164.40	$164.40
Purchase #5	$7.34	3.268%	$7.5799	$7.58	$7.60	$7.60
Purchase #6	$108.27	9.791%	$118.8707	$118.87	$118.85	$118.90
Purchase #7	$34.45	5.280%	$36.269	$36.27	$36.25	$36.30
7 purchase totals =	$842.51		$894.3724	$894.37	$894.35	$894.40