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	$57.71	11.145%	$64.1418	$64.14	$64.15	$64.10
Purchase #2	$63.43	6.751%	$67.7122	$67.71	$67.70	$67.70
Purchase #3	$201.73	6.743%	$215.3327	$215.33	$215.35	$215.30
Purchase #4	$116.84	12.825%	$131.8247	$131.82	$131.80	$131.80
Purchase #5	$156.72	4.630%	$163.9761	$163.98	$164.00	$164.00
Purchase #6	$36.82	10.259%	$40.5974	$40.60	$40.60	$40.60
Purchase #7	$215.60	12.225%	$241.9571	$241.96	$241.95	$242.00
7 purchase totals =	$848.85		$925.5420	$925.54	$925.55	$925.50