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	$166.34	11.693%	$185.7901	$185.79	$185.80	$185.80
Purchase #2	$245.59	3.524%	$254.2446	$254.24	$254.25	$254.20
Purchase #3	$40.62	11.751%	$45.3933	$45.39	$45.40	$45.40
Purchase #4	$52.79	7.621%	$56.8131	$56.81	$56.80	$56.80
Purchase #5	$74.95	9.574%	$82.1257	$82.13	$82.15	$82.10
Purchase #6	$29.51	8.264%	$31.9487	$31.95	$31.95	$31.90
Purchase #7	$161.68	12.268%	$181.5149	$181.51	$181.50	$181.50
7 purchase totals =	$771.48		$837.8304	$837.82	$837.85	$837.70