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	$84.55	7.289%	$90.7128	$90.71	$90.70	$90.70
Purchase #2	$51.33	5.873%	$54.3446	$54.34	$54.35	$54.30
Purchase #3	$93.98	5.649%	$99.2889	$99.29	$99.30	$99.30
Purchase #4	$170.43	3.421%	$176.2604	$176.26	$176.25	$176.30
Purchase #5	$55.43	11.805%	$61.9735	$61.97	$61.95	$62.00
Purchase #6	$175.86	4.718%	$184.1571	$184.16	$184.15	$184.20
Purchase #7	$155.86	12.177%	$174.8391	$174.84	$174.85	$174.80
7 purchase totals =	$787.44		$841.5764	$841.57	$841.55	$841.60