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	$73.34	9.706%	$80.4584	$80.46	$80.45	$80.50
Purchase #2	$59.51	3.263%	$61.4518	$61.45	$61.45	$61.50
Purchase #3	$166.88	6.623%	$177.9325	$177.93	$177.95	$177.90
Purchase #4	$96.46	12.537%	$108.5532	$108.55	$108.55	$108.60
Purchase #5	$27.52	4.653%	$28.8005	$28.80	$28.80	$28.80
Purchase #6	$247.53	9.264%	$270.4612	$270.46	$270.45	$270.50
Purchase #7	$184.69	6.162%	$196.0706	$196.07	$196.05	$196.10
7 purchase totals =	$855.93		$923.7282	$923.72	$923.70	$923.90