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	$54.25	5.529%	$57.2495	$57.25	$57.25	$57.20
Purchase #2	$115.54	8.564%	$125.4348	$125.43	$125.45	$125.40
Purchase #3	$40.52	7.524%	$43.5687	$43.57	$43.55	$43.60
Purchase #4	$131.70	4.531%	$137.6673	$137.67	$137.65	$137.70
Purchase #5	$88.75	8.282%	$96.1003	$96.10	$96.10	$96.10
Purchase #6	$75.59	10.275%	$83.3569	$83.36	$83.35	$83.40
Purchase #7	$113.37	8.618%	$123.1402	$123.14	$123.15	$123.10
7 purchase totals =	$619.72		$666.5177	$666.52	$666.50	$666.50