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	$190.88	8.329%	$206.7784	$206.78	$206.80	$206.80
Purchase #2	$67.96	4.711%	$71.1616	$71.16	$71.15	$71.20
Purchase #3	$103.35	12.175%	$115.9329	$115.93	$115.95	$115.90
Purchase #4	$116.60	12.468%	$131.1377	$131.14	$131.15	$131.10
Purchase #5	$249.74	12.118%	$280.0035	$280.00	$280.00	$280.00
Purchase #6	$57.27	9.151%	$62.5108	$62.51	$62.50	$62.50
Purchase #7	$94.51	4.801%	$99.0474	$99.05	$99.05	$99.00
7 purchase totals =	$880.31		$966.5723	$966.57	$966.60	$966.50