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	$107.59	11.424%	$119.8811	$119.88	$119.90	$119.90
Purchase #2	$225.89	12.300%	$253.6745	$253.67	$253.65	$253.70
Purchase #3	$75.60	9.135%	$82.5061	$82.51	$82.50	$82.50
Purchase #4	$187.25	13.702%	$212.907	$212.91	$212.90	$212.90
Purchase #5	$97.84	4.584%	$102.325	$102.33	$102.35	$102.30
Purchase #6	$215.79	5.751%	$228.2001	$228.20	$228.20	$228.20
Purchase #7	$82.32	9.761%	$90.3553	$90.36	$90.35	$90.40
7 purchase totals =	$992.28		$1,089.8491	$1,089.86	$1,089.85	$1,089.90