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	$121.26	8.149%	$131.1415	$131.14	$131.15	$131.10
Purchase #2	$140.46	3.275%	$145.0601	$145.06	$145.05	$145.10
Purchase #3	$20.53	6.298%	$21.823	$21.82	$21.80	$21.80
Purchase #4	$40.25	13.627%	$45.7349	$45.73	$45.75	$45.70
Purchase #5	$237.78	9.321%	$259.9435	$259.94	$259.95	$259.90
Purchase #6	$27.75	3.418%	$28.6985	$28.70	$28.70	$28.70
Purchase #7	$198.50	10.402%	$219.148	$219.15	$219.15	$219.10
7 purchase totals =	$786.53		$851.5495	$851.54	$851.55	$851.40