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	$234.90	12.107%	$263.3393	$263.34	$263.35	$263.30
Purchase #2	$131.35	6.495%	$139.8812	$139.88	$139.90	$139.90
Purchase #3	$96.33	3.613%	$99.8104	$99.81	$99.80	$99.80
Purchase #4	$80.87	10.778%	$89.5862	$89.59	$89.60	$89.60
Purchase #5	$187.88	12.228%	$210.854	$210.85	$210.85	$210.90
Purchase #6	$110.45	10.504%	$122.0517	$122.05	$122.05	$122.10
Purchase #7	$246.88	13.776%	$280.8902	$280.89	$280.90	$280.90
7 purchase totals =	$1,088.66		$1,206.4130	$1,206.41	$1,206.45	$1,206.50