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	$236.89	9.417%	$259.1979	$259.20	$259.20	$259.20
Purchase #2	$101.38	12.346%	$113.8964	$113.90	$113.90	$113.90
Purchase #3	$241.36	13.693%	$274.4094	$274.41	$274.40	$274.40
Purchase #4	$167.60	4.337%	$174.8688	$174.87	$174.85	$174.90
Purchase #5	$122.64	12.151%	$137.542	$137.54	$137.55	$137.50
Purchase #6	$76.81	9.309%	$83.9602	$83.96	$83.95	$84.00
Purchase #7	$104.59	13.123%	$118.3153	$118.32	$118.30	$118.30
7 purchase totals =	$1,051.27		$1,162.1900	$1,162.20	$1,162.15	$1,162.20