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	$25.57	5.858%	$27.0679	$27.07	$27.05	$27.10
Purchase #2	$217.79	3.414%	$225.2254	$225.23	$225.25	$225.20
Purchase #3	$221.38	13.510%	$251.2884	$251.29	$251.30	$251.30
Purchase #4	$213.55	9.148%	$233.0856	$233.09	$233.10	$233.10
Purchase #5	$79.73	12.746%	$89.8924	$89.89	$89.90	$89.90
Purchase #6	$52.31	6.158%	$55.5312	$55.53	$55.55	$55.50
Purchase #7	$89.96	7.508%	$96.7142	$96.71	$96.70	$96.70
7 purchase totals =	$900.29		$978.8051	$978.81	$978.85	$978.80