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	$45.60	12.329%	$51.222	$51.22	$51.20	$51.20
Purchase #2	$114.95	12.512%	$129.3325	$129.33	$129.35	$129.30
Purchase #3	$250.39	11.862%	$280.0913	$280.09	$280.10	$280.10
Purchase #4	$196.49	9.689%	$215.5279	$215.53	$215.55	$215.50
Purchase #5	$79.33	5.549%	$83.732	$83.73	$83.75	$83.70
Purchase #6	$115.59	6.799%	$123.449	$123.45	$123.45	$123.40
Purchase #7	$11.93	12.624%	$13.436	$13.44	$13.45	$13.40
7 purchase totals =	$814.28		$896.7907	$896.79	$896.85	$896.60