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	$54.37	4.857%	$57.0108	$57.01	$57.00	$57.00
Purchase #2	$213.54	9.119%	$233.0127	$233.01	$233.00	$233.00
Purchase #3	$211.73	6.473%	$225.4353	$225.44	$225.45	$225.40
Purchase #4	$59.28	13.597%	$67.3403	$67.34	$67.35	$67.30
Purchase #5	$166.89	13.865%	$190.0293	$190.03	$190.05	$190.00
Purchase #6	$36.51	9.661%	$40.0372	$40.04	$40.05	$40.00
Purchase #7	$228.32	13.610%	$259.3944	$259.39	$259.40	$259.40
7 purchase totals =	$970.64		$1,072.2600	$1,072.26	$1,072.30	$1,072.10