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	$44.62	12.323%	$50.1185	$50.12	$50.10	$50.10
Purchase #2	$41.61	5.606%	$43.9427	$43.94	$43.95	$43.90
Purchase #3	$81.48	12.167%	$91.3937	$91.39	$91.40	$91.40
Purchase #4	$56.79	4.780%	$59.5046	$59.50	$59.50	$59.50
Purchase #5	$220.57	12.516%	$248.1765	$248.18	$248.20	$248.20
Purchase #6	$23.84	13.468%	$27.0508	$27.05	$27.05	$27.10
Purchase #7	$29.93	5.127%	$31.4645	$31.46	$31.45	$31.50
7 purchase totals =	$498.84		$551.6513	$551.64	$551.65	$551.70