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	$52.90	8.397%	$57.342	$57.34	$57.35	$57.30
Purchase #2	$249.81	12.465%	$280.9488	$280.95	$280.95	$280.90
Purchase #3	$96.98	12.554%	$109.1549	$109.15	$109.15	$109.20
Purchase #4	$80.56	4.144%	$83.8984	$83.90	$83.90	$83.90
Purchase #5	$56.51	4.131%	$58.8444	$58.84	$58.85	$58.80
Purchase #6	$19.41	10.793%	$21.5049	$21.50	$21.50	$21.50
Purchase #7	$235.81	13.160%	$266.8426	$266.84	$266.85	$266.80
7 purchase totals =	$791.98		$878.5360	$878.52	$878.55	$878.40