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	$103.51	5.281%	$108.9764	$108.98	$109.00	$109.00
Purchase #2	$126.86	7.139%	$135.9165	$135.92	$135.90	$135.90
Purchase #3	$128.35	7.162%	$137.5424	$137.54	$137.55	$137.50
Purchase #4	$104.38	4.745%	$109.3328	$109.33	$109.35	$109.30
Purchase #5	$73.92	5.681%	$78.1194	$78.12	$78.10	$78.10
Purchase #6	$28.70	12.577%	$32.3096	$32.31	$32.30	$32.30
Purchase #7	$202.86	7.336%	$217.7418	$217.74	$217.75	$217.70
7 purchase totals =	$768.58		$819.9389	$819.94	$819.95	$819.80